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Climatological analysis of Mediterranean cyclones using ECMWF Data
Abstract
ABSTRACTA thoroughly objective method for the definition, selection and tracing of Mediterranean region cyclones is presented. The method is applied to the ECMWF 1982-1987 analyzed datasets to show monthly cyclone frequencies, cyclonic tracks and vertical variation of average relative vorticity. Day-to-night changes and vertical variation of cyclonic frequencies/vorticities indicate the importance of the sea thermal effect in the eastern Mediterranean. In the western Mediterranean and to a lesser extent in the Cyprus region, the lee cyclogenetic effect is very pronounced. Monthly cyclone tracks are presented and they clearly indicate the preferred routes of cyclonic movements.
... Then, the position of the low centers for the stormy days was on 1000-hPa pressure level for the domain bounded by 24 °N-60 °N latitudes and 0 °E-55 °E longitudes. The location of centers is computed by using parabolic interpolation after determining the candidate grid that has a geopotential height value less than or equal to a geopotential height value of surrounding grids as described in Alpert et al. (1990). The meander of geopotential heights of stormy days is overlayed for the same domain. ...
... An averaged low center is seen over Italy and the Adriatic Sea while the averaged high center is located at the southeast part of Turkey, Iraq, and Iran for 10 years with 24-m and 174-m geopotential heights, respectively. A similar methodology has been applied for the relative vorticity by Alpert et al. (1990). The low center of the 1000-hPa averaged pattern may have an impact on Greece, Bulgaria, and northwest Turkey. ...
... An averaged low center is seen over Italy and the Adriatic Sea while the averaged high center is located in the southeast part of Turkey, Iraq, and Iran for 10 years during these 87 stormy days. A similar methodology has been applied for the relative vorticity by Alpert et al. (1990). The low center of the 1000-hPa averaged pattern may have an impact on Greece, Bulgaria, and northwest Turkey. ...
The study aims to understand the reasons for southerly wind storms affecting the Marmara region of Turkey for 2000-2010 and to present their patterns related to synoptic weather systems. In this study, a day with the wind speed exceeding 15.5 m/s and observed at least 1h at any station in the region is called a "stormy day". The number of wind storms was examined based on their annual and monthly distribution and frequencies. It was also found that about 99% of the southern wind storms over the Marmara region of Turkey are related to the frontal systems such as passing or approaching the fronts and sector approaches. The wind storms have occurred with 56.3%,27.6%,and 16.1% in winter, spring, and fall, respectively. No strong wind storms were detected in the summer months.
... The overall spatial distribution of our data set is in agreement with previous studies (Alpert et al., 1990;Trigo et al., 1999;Maheras et al., 2001;Campins et al., 2011;Lionello et al., 2016;Aragão and Porcù, 2022;Flaounas et al., 2023). However, two minor differences remain. ...
... In the East Mediterranean, more cyclones are also found during the cold part of the year. Saharan cyclones clearly exhibit a peak of occurrence in April and May, in agreement with previous studies (Winstanley, 1972;Alpert et al., 1990;Trigo et al., 2002). The Black Sea has a unique seasonal cycle, with higher activity during a long period spanning from December to July with a peak in March. ...
Mediterranean cyclones are essential components of the climate in a densely populated area, providing beneficial rainfall for both the environment and human activities. The most intense of them also lead to natural disasters because of their strong winds and heavy precipitation. Identifying error sources in the predictability of Mediterranean cyclones is therefore essential to better anticipate and prevent their impact. The aim of this work is to characterise the cyclone predictability in this region. Here, it is investigated in a systematic framework using European Centre for Medium range Weather Forecasting (ECMWF) fifth generation reanalysis (ERA5) and ensemble reforecasts in a homogeneous configuration over 20 years (2001–2021). First, a reference data set of 2853 cyclones is obtained for the period by applying a tracking algorithm to the ERA5 reanalysis. Then the predictability is systematically evaluated in the ensemble reforecasts. It is quantified using a new probabilistic score based on the error distribution of cyclone location and intensity (mean sea level pressure). The score is firstly computed for the complete data set and then for different categories of cyclones based on their intensity, deepening rate, velocity and on the geographic area and the season in which they occur. When crossing the location and intensity errors with the different categories, the conditions leading to a poorer or better predictability are discriminated. The velocity of cyclones appears to be determinant in the predictability of the location, the slower the cyclone the better the forecast location. Particularly, the position of stationary lows located in the Gulf of Genoa is remarkably well predicted. The intensity of deep and rapid-intensification cyclones, occurring mostly during winter, is for its part particularly poorly predicted. This study provides the first systematic evaluation of the cyclone predictability in the Mediterranean and opens the way to identify the key processes leading to forecast errors in the region.
... The mountain range bounds the Mediterranean Sea, and its water is warmer than in the adjacent Atlantic Ocean. Alpert et al. (1990aAlpert et al. ( , 1990b and Maheras et al. (2001) found that the thermal processes of the Mediterranean Sea affected the cyclogenesis of the eastern Mediterranean and the path of these cyclones that passed through the prominent mountains limiting the Mediterranean Sea. The Mediterranean cyclones are complex because of orographic effects and recreation on the sea. ...
... The precipitation associated with this system affected Iran, the eastern Mediterranean, and Turkey (Fenodi et al., 2017). Several investigations have been conducted to investigate this system (Alpert, 2004;Alpert et al., 1990aAlpert et al., , 1990bBitan & Saaroni, 1992;Dayan & Abramsky, 1983;Fenodi et al., 2017;Flocas et al., 2010;Jahanbakhsh et al., 2020;Kahana et al., 2002;Kidron & Pick, 2000;Mofidi & Zarin, 2005;Mohammadi & Lashkari, 2018;Parak et al., 2016). Irannejad et al. (2009) studied the annual frequency of cyclone centers on Iran's annual precipitation from 1960 through 2002. ...
In the current study, the decadal changes in Iran's precipitation regimes (PRs) were investigated by adopting Iran's precipitation dataset and using the precipitation index (PI). Our finding revealed that significant decadal variation occurred in the PI, which led to different spatial patterns during under investigation decades. From the 1st to last decades under study, the area decreased in the regions with equal monthly distribution of precipitation (ED). The regions with a relatively equal monthly concentration of precipitation (RED) presented a sharp decreasing trend in the first 3 decades and a slight increase in the last decade. The irregular distribution of precipitation (ID) in most of the decades covered an area above the long-term average. The highly irregular distribution of precipitation (HID) covered a small area of Iran's territory on the southern coasts. Nevertheless, its decadal variation, particularly in the first 3 decades, was relatively noticeable. The decadal variability of the number and tracks of cyclones affecting Iran showed that although the number of cyclones increased from the 1st to the last decade, the origins of cyclones in the 1st decade were mainly in the Mediterranean Sea and the Red Sea. In the following decades, the diversity of the origins of the cyclones was one of the decades' characteristics. In addition, from the 1st to 3rd decade, the cyclone centers (excluding the Red Sea-Sudanese cyclones) took a more northerly route. This decadal variation in cyclones' characteristics might lead to the decadal variation of PI in Iran.
... Ainsi se forme une cellule dynamique au dessous du jet-streak ; en aval une ascendance de l'air, chaud et humide, depuis la surface jusqu'au jet-stream; en amontune intrusion de l'air stratosphérique, sec et froid et qui descend vers la surface (Joly, 2003 ;Baehr, 1999 ;Hoskins, 2006 ). Dans ce contexte, d'après la théorie Storm-Track, le jet-stream subtropical peut donc générer une cyclogenèse saharienne quand il présente une forte zone de confluence en altitude (Alpert et al. 1990;Trigo et al. 1998). Ceci explique, dans certain cas, la formation de la cyclogenèse au Sud de la Tunisie, sur le Golfe de Gabès (Bonvallot, 1986), au-dessus de la Lybie, l'Egypte (Moulin et al. 1998, Trigo et al. 2002, la mer rouge (Uri Dayan and Efrat 42 Morin, 2006) et le moyen Orient (Kahana et al. 2004). ...
... Elle est crée quand le jet-stream polaire se déplace vers le Sud et regagne les littorales africaines où s'il se connecte au jet-stream subtropical. D'après la théorie Strom-Track, le jet-stream subtropical peut aussi générer une cyclogenèse saharienne quand il présente une zone de diffluence en altitude (Alpert et al. 1990;Trigo et al. 1998). Ceci explique la formation de la cyclogenèse au Sud de la Tunisie, au Golfe de Gabes (Bonvallot, 1986), au-dessus de la Lybie, l'Egypte (Moulin et al. 1998, Trigo et al. 2002, la mer rouge (Uri Dayan and Efrat Morin, 2006) et le moyen Orient (Kahana et al. 2004). ...
Dans le cadre de la gestion des risques, il est important de mieux connaître les régimes du temps caractérisés par des évènements et des phénomènes météorologiques exceptionnels, particulièrement la cyclogenèse. Dans ce contexte, nous nous sommes intéressés à l’étude de la cyclogenèse en Méditerranée qui est un sujet très intéressant pour les chercheurs et les projets d’étude et de développement. Nous avons commencé par étudier la physique et les théories de la cyclogenèse en nous basant sur les équations dynamiques de l’atmosphère, les principes des grands équilibres synoptiques, la notion de la vorticité, le jet-stream, la théorie de la frontogenèse, la théorie de l’interaction barocline et la théorie Storm-Track. Pour comprendre les mécanismes responsables de la cyclogenèse en Méditerranée, nous avons étudié ses problématiques ainsi que les modèles conceptuels descriptives de la genèse des cyclones. Pour approfondir nos connaissances et en plus de la simulation réalisée par le modèle ALADIN, nous avons adapté le modèle MM5V3 numérique à maille fine au domaine méditerranéen dans le but de réaliser des simulations et des tests de sensibilité. Après une présentation du modèle MM5V3 et ses principales caractéristiques, nous avons présenté sa chaîne d’exploitation, l’utilisation du système complet du modèle, ainsi que l’ordre des programmes qui sont présentés par un diagramme avec une brève description de leurs fonctions principales. Nous avons jugé les résultats du modèle MM5V3 positifs. En effet ces résultats sont en accord avec les observations. Les budgets énergétiques et pluviométriques estimés par le modèle prouvent la bonne para-métrisation physique des processus dynamiques et thermiques présents. Le modèle a aussi bien estimé les effets locaux de la région. Nous avons choisit la vorticité potentielle (VP) comme outil principal dans nos analyses car c’est un bon marqueur des centres d’actions et de leurs effets. Toutes les informations sont aussi contenues dans la VP ce qui offre une vue d’ensemble synthétique de tous les processus physiques et de leurs interactions.
... It is found that coastal inundation events are usually caused by enfeebled extra-tropical cyclones following the South-European extension of the North Atlantic storm tracks or by secondary triggered cyclones in the north-western Mediterranean basin (cyclogenetic centre of the Gulf of Lions). The North-African cyclogenesis centre can also produce deep depressions pronounced in the east-central Mediterranean probably affected by climate change signals mid-latitude storm tracks and their Mediterranean branches towards the Adriatic, Ionian, and Aegean Seas (Alpert et al., 1990;Trigo et al., 1999;Maheras et al., 2001;Flaounas et al., 2018;Lionello et al., 2016;Reale and Lionello, 2013). The main centres of cyclogenesis around and over the Mediterranean Sea are the Genoa aera, the Saharan cyclonic regions (mainly during spring), the Iberian Peninsula thermal lows, the Aegean Sea (during winter and spring), the eastern Black Sea region (enhanced during summer), the leeward regions of the Alps and Atlas Mountains, the Cyprus cyclone source, and the Middle Eastern centre over Syria (as an extension of the Indian Monsoon low) (Maheras et al., 2001;Makris et al., 2016). ...
... However, at first, their identification and localization were mostly based on empirical methods, including the subjectivity of researchers (Maheras, 1983;Radinovic, 1987;Flocas, 1988). Later, and since the 1990's, more objective methodologies were utilized to detect these centres of cyclogenesis at several domains of interest (e.g., Alpert et al., 1990;Trigo et al., 1999;Maheras et al., 2001;Flaounas et al., 2018) over and around the basin. According to relevant literature (Flocas and Karacostas, 1996;Thorncroft and Flocas, 1997;Trigo et al., 1999;Maheras et al., 2001;Lionello et al., 2016) the main areas, characterized as ''Cyclogenesis Centres'', related to the Mediterranean domain are the following: ...
This study aims to systematically assess the impacts of projected climate change on episodic events of sea level elevation in coastal areas of the Mediterranean, induced by severe weather conditions identified as deep depressions. We try to add new insight in the long-term, climatic timescale, identification of affected parts of the Mediterranean coastal zone correlated to low atmospheric pressure systems, indicative of the Mediterranean basin during the 21st century. To achieve this goal, an integrated quantitative assessment is proposed by combining projections from available and established, green-house gasses emission/concentration scenarios (based on Representative Concentration Pathways; RCP 4.5 and 8.5) with advanced numerical modelling and statistical post-processing for the definition of cyclonic weather impacts on characteristic coastal zone hotspots. To this end, climate projections and outputs from three Regional Climate Models (RCMs) of the Med-CORDEX initiative at the Mediterranean basin scale are used and extensively evaluated against re-analysis data. These atmospheric datasets feed a robust storm surge model (MeCSS) for the simulation of barotropic hydrodynamics (sea level elevation and currents) thoroughly validated against in situ sea level observations by tide-gauges. Our results corroborate a projected storminess attenuation for the end of the 21st century, yet local differentiations in storm surge maxima around the Mediterranean coastal zone are pinpointed. Moreover, a slight reduction of average storm-induced Mean Sea Level (MSL; component attributed solely to the meteorological residual of sea level elevation) is also apparent towards the end of the 21st century. Extreme storm surge magnitudes range between 0.35 and 0.50 m in the Mediterranean with higher values along parts of its northern coasts (Venice lagoon, Gulf of Lions, northern Adriatic and Aegean Seas, etc.) and the Gulf of Gabes in its southern part. Overall, the spatial distributions of surge maxima are estimated to remain similar to those of the past throughout the entire Mediterranean coastal zone. Differentiations between the two scenarios (RCP4.5-8.5) used are obvious, not so much related to the spatiotemporal distribution of storm surge maxima, which shows a very stable pattern, but more in terms of their magnitudes. Indicatively, a decrease of surge maxima from -30% to -2% can be observed towards the end of the 21st century, especially for RCP8.5-driven MeCSS simulations. This is a spatially averaged estimation, yet for some specific coastal sites in Croatia, Spain Italy, and France, such as Rovinj, Bakar, Toulon, Trieste, Ajaccio, Genova, Marseilles, Naples, Venice, Cagliari, Ancona, Ibixa, and Barcelona, the storm surge maxima might increase from 1% to 22% under different RCM/RCP combinations towards the end of the 21st century. Our analysis leads to the quantification of deep depression systems’ effect on the coastal sea level elevation due to storm surges towards 2100. The strongest correlations of deep depression events to high sea levels are observed in several parts along the northern Mediterranean coasts (Gulfs of Valencia and Lions, Ligurian and northern Adriatic Seas). They are followed by mid-latitude areas around Corsica, Sardinia, the mid-zonal Italian Peninsula and the Adriatic, and the northern Aegean Sea. The influence of deep depressions on storm surges is lower for Sicily, South Italy, Peloponnese, Crete, the southern Aegean archipelago, and Alboran Sea. The only exceptions in the generally unaffected southern Mediterranean littorals are the Gulfs of Gabes and Alexandretta. These apply to the 20th century; however, they seem to repeat for the 21st century estimations, with even more pronounced differentiations between the southern and the northern parts. A projected northward shift of the main deep depression centres over the Mediterranean towards the end of the 21st century, is likely the reason for the latter. The climate change signal (difference of Future – Reference Period) of the deep cyclones’ effect on the episodic increases of coastal sea level seems to have a very clear pattern of slight attenuation in certain regions, i.e., Sardinia, Corsica, the Ligurian and Adriatic Seas, and the entire Italian peninsula for all RCM-fed implementations towards the end of the 21st century. Conditionally, this is the case for the Gulf of Valencia, the north-western African coasts, the Alboran, Ionian, Aegean, and Libyan Sea coasts, under specific combinations of RCM/RCP forcings. On the other hand, a possible increase of the Mediterranean deep depressions’ influence on the coastal storm surges might be the case for the Gulf of Lions, the Ionian, Aegean and Levantine Sea basins, covering the north-central and north-eastern coasts of Africa. In general, a positive influence of deep depressions to storm surge maxima would probably refer to areas of mid-to-high storm surge maxima (e.g., Aegean, Ionian, Gulf of Lions or Valencia or Gabes, etc.), but not the highest throughout the basin (e.g., Venice lagoon, Ligurian, Adriatic, etc.). In the latter coastal regions, however, intense local wind forcing mechanisms (i.e., Scirocco) are bound to play an essential role in the formation of high storm surges. The produced results can be used in focused studies for integrated hydrologic/hydrodynamic modelling under projected climate change conditions in the 21st century.
... 2.1 Spatial variability in and seasonal cycle of Mediterranean cyclone tracks Alpert et al. (1990) performed one of the first studies focusing on the climatology of Mediterranean cyclones. The authors used a 5-year (1983-1987) climatological dataset of ECMWF operational analyses with a grid spacing of 2.5 • × 2.5 • and a time interval of 12 h. ...
... Cyclones around Cyprus, usually called Cyprus Lows (e.g. Alpert et al., 1990;Flocas et al., 2010;Ulbrich et al., 2012), play a fundamental role in shaping the variability in precipitation in the eastern Mediterranean basin (Goldreich, 2003;Saaroni et al., 2010;Hochman et al., 2018). Autumn and spring are transitional periods for cyclogenesis frequency, sharing to some extent similar characteristics with the climatological spatial variability of winter. ...
A large number of intense cyclones occur every year in the Mediterranean basin, one of the climate change hotspots. Producing a broad range of severe socio-economic and environmental impacts in such a densely populated region, Mediterranean cyclones call for coordinated and interdisciplinary research efforts. This article aims at supporting these efforts by reviewing the status of knowledge in the broad field of Mediterranean cyclones.
First, we focus on the climatology of Mediterranean cyclone tracks, their relationship to large-scale atmospheric circulation and their future trends. Second, we discuss the dynamics and atmospheric processes that govern the genesis and development of Mediterranean cyclones. Then, we present the different subtypes of Mediterranean cyclones, devoting special attention to medicanes, i.e. cyclones with tropical characteristics and subjects of numerous recent studies. In a subsequent section, we review the state of the art in forecasting cyclones and relevant high-impact weather, and we discuss in detail the challenges and recent efforts to increase their forecast skill. Finally, we discuss the main impacts produced by cyclones, namely heavy precipitation, windstorms, dust transport, storm surges and sea wave extremes.
In the last section of this review article, we thoroughly outline the future directions of research that would advance the broader field of Mediterranean cyclones.
... Deep convection acts as a source of potential vorticity for the cyclone (see Flaounas et al. 2021a, b). Past studies have identified several cyclogenetic areas in the region: the Atlas Mountains, the Gulf of Genoa, the Aegean Sea, the Iberian peninsula, the Black Sea and the Eastern Mediterranean (Alpert et al. 1990;Trigo et al. 1999;Lionello et al. 2006Lionello et al. , 2016Campins et al. 2010;Flaounas et al. 2018Flaounas et al. , 2021bBuzzi et al. 2020). Moreover, approximately 11% of cyclones moving across the region originate in the Atlantic Ocean (Lionello et al. 2016). ...
... Relative maxima are captured in the Gulf of Genoa, Western Mediterranean, North Africa and in proximity to Cyprus in agreement with previous studies (e.g. Alpert et al. 1990;Trigo et al. 1999;Lionello et al. 2006Lionello et al. , 2016Campins et al. 2010;Ulbrich et al. 2012;Flaounas et al. 2018). The spatial correlation coefficient between each RCSM and ERA5 is high, ranging from 0.73 (CNRM-RCSM4) to 0.89 (LMD-CNRM). ...
Here, we analyze future projections of cyclone activity in the Mediterranean region at the end of the twenty-first century based on an ensemble of state-of-the-art fully-coupled Regional Climate System Models (RCSMs) from the Med-CORDEX initiative under the Representative Concentration Pathway (RCP) 8.5. Despite some noticeable biases, all the RCSMs capture spatial patterns and cyclone activity key characteristics in the region and thus all of them can be considered as plausible representations of the future evolution of Mediterranean cyclones. In general, the RCSMs show at the end of the twenty-first century a decrease in the number and an overall weakening of cyclones moving across the Mediterranean. Five out of seven RCSMs simulate also a decrease of the mean size of the systems. Moreover, in agreement with what already observed in CMIP5 projections for the area, the models suggest an increase in the Central part of the Mediterranean region and a decrease in the South-eastern part of the region in the cyclone-related wind speed and precipitation rate. These rather two opposite tendencies observed in the precipitation should compensate and amplify, respectively, the effect of the overall reduction of the frequency of cyclones on the water budget over the Central and South-eastern part of the region. A pronounced inter-model spread among the RCSMs emerges for the projected changes in the cyclone adjusted deepening rate, seasonal cycle occurrence and associated precipitation and wind patterns over some areas of the basin such as Ionian Sea and Iberian Peninsula. The differences observed appear to be determined by the driving Global Circulation Model (GCM) and influenced by the RCSM physics and internal variability. These results point to the importance of (1) better characterizing the range of plausible futures by relying on ensembles of models that explore well the existing diversity of GCMs and RCSMs as well as the climate natural variability and (2) better understanding the driving mechanisms of the future evolution of Mediterranean cyclones properties.
... This section provides an overview of the main results of these efforts, focusing on the climatology of cyclone tracks, the different cyclone types that develop in the region and their future trends. Alpert et al. (1990) performed one of the first studies focusing on the climatology of Mediterranean cyclones. The authors used a 5-year (1983)(1984)(1985)(1986)(1987) climatological dataset of ECMWF operational analyses with a grid spacing of 2.5°x2.5° ...
... Cyclones around Cyprus, usually called Cyprus Lows (e.g. Alpert et al. 1990;Flocas et al., 2010;Ulbrich et al., 2012), play a fundamental role in shaping the variability of precipitation in the eastern Mediterranean basin (Goldreich 2003;Saaroni et al., 2010;Hochman et al., 2019). Autumn and spring are transitional periods for cyclogenesis frequency, sharing to some extent similar characteristics with the climatological spatial variability of winter. ...
A large number of intense cyclones occur every year in the Mediterranean basin, one of the climate change hotspots. Producing a broad range of severe socio-economic and environmental impacts in such a densely populated region, Mediterranean cyclones call for coordinated and interdisciplinary research efforts. This article aims at supporting these efforts by reviewing the status of knowledge in the broad field of Mediterranean cyclones. First, we focus on the dynamics and atmospheric processes that govern the genesis and development of Mediterranean cyclones. Then, we review the state of the art in forecasting cyclones and relevant high-impact weather. Particular attention is given to Mediterranean cyclone tracks and their physical characteristics in current and future climate. Finally, we focus on the impacts produced by cyclones and we outline the future directions of research that would advance the broader field of Mediterranean cyclones as a whole.
... Cyprus Lows (CLs), which are mid-latitude cyclones (Alpert et al. 1990;Ulbrich et al. 2012), are the major rain contributors in Israel, and are responsible for 90% of the annual rainfall (Goldreich et al. 2004). A significant correlation was found between the number of CL days and the annual rainfall in the Mediterranean and semi-arid climate regions of Israel . ...
... A positive MOI2 implies a southward shift of the upper level isohypses over the EM, leading to a southward shift of the CL tracks, which enhances their influence on south Israel. This effect is minor for north Israel, which is almost always close to the average CL track, located north of the study area (e.g., Alpert et al. 1990). ...
Previous observational analyses have shown a declining rainfall trend over Israel, mostly statistically insignificant. The current study, for the period 1975–2020, undermines these findings, and the alarming future projections, and elaborates other ingredients of the rain regime. No trend is found for the annual rainfall, reflecting a balance between a negative trend in the number of rainy days and a positive trend in the daily rainfall intensity, both on the order of 2.0%/decade. In the mid-winter, the rainfall and the daily intensity increased, while both declined in the autumn and spring, implying a contraction of the rainy season. The time span between accumulation of 10% and 90% of the annual rainfall, being 112 days on the average, shortened by 7 days during the study period. This is also expressed by an increase of the Seasonality Index, indicating that the regional climate is shifting from “markedly seasonal with a long dry season” to “most rain in ≤3 months.” The intra-seasonal course of the rainfall trend corresponds to that of the occurrence and intensity of the Cyprus Lows and the Mediterranean Oscillation. The contraction of the rainy season and the increase in the daily intensity have far-reaching environmental impacts in this vulnerable region.
... The Mediterranean cyclones, and the CLs as well, resemble features of mid-latitude cyclones , which implies that they are linked to upper-level cyclonic systems. However, the CLs were shown to exhibit diurnal variation, that is, during the night they tend to appear over the warmer water of the EM and strengthen, and during the day, to deviate to the north, to the lee of the Taurus mountains in southern Turkey (Alpert et al., 1990). ...
... It goes in line with diurnal variations found in the RST (Saaroni et al., 2020), expressed by its westward shift towards the warmer sea during nighttime and inland during daytime (~5 longitudes distance in the average location), and its double occurrence during nighttime compared to noontime. Moreover, a tendency of CLs to appear and be stronger over the relative warm F I G U R E 1 3 As in Figure 6, but for events of type 3iv: An upper-level trough located east of 20 E moving at a speed of <8 ms −1 [Colour figure can be viewed at wileyonlinelibrary.com] water of the EM during nighttime, and to shift towards the adjacent land during daytime, was found by Alpert et al. (1990). ...
The Red‐Sea Trough (RST) is a lower‐level trough extending from the tropical low‐pressure to the Levant. Its annual occurrence in the Levant is 20%, mostly in the autumn. It produces dry weather, but occasionally causing local showers and floods. During winter, the dominant synoptic system over the eastern Mediterranean is the Cyprus low (CL). Previous studies showed that some CLs form within pre‐existing RSTs, through a tropical–extratropical interaction.
This study is the first comprehensive climatological framework of such formation events, analyzing their occurrence, seasonality, and the resulting rainfall in Israel. The study identified and analyzed CLs formed within the domain 31°–35°N, 30°–36°E within an RST that was detected during the preceding 24 hr. We used the 6‐hourly ERA‐Interim database, with 0.75° × 0.75° resolution, during 1979–2017, and identified 104 formation events, which constitute 10% of the CLs. Most formation events occur during fall and early winter, similarly to the RST. Eighty four percent of them formed during the evening or night, and almost two thirds of the CLs disappeared temporarily at noon and regenerated afterwards. This is attributed to the sea/land diurnal oscillation. Most of the formed CLs were shallow, with little rain, but some became major storms, like ‘Alexa’, which caused extreme snowing in Jerusalem, in December 2013. The formation scenarios were divided into four categories, according to the location and propagation of the 500‐hPa trough. The first is characterized by a closed cyclone approaching from southwest, often connected to active RSTs. In the second, a trough is deepening from the northern sector, possibly a polar intrusion. In the third, the most populated, a trough is approaching from west. The fourth category contains events with no upper‐level support. Composite maps indicate that upper‐level positive vorticity advection triggered CL formations, on top of pre‐existing above‐normal lower‐level temperatures, imparted by the RST.
... As a critical first step for reconstructing LIG climate, the conditions which can induce d-excess variability in modern accumulated rainfall were examined. Today,~90% of rainfall in central and northern Israel is derived from mid-latitude Cyprus Low (CL) cyclones, where cold air mainly originating over southern Europe gathers moisture from the warm Mediterranean water before entering Israel from the west (Fig. 1B) [47][48][49][50] . The rainfall season is confined to October-May, and around two-thirds of the annual rainfall occurs during December-February 50 . ...
There is limited understanding of temperature and atmospheric circulation changes that accompany an Atlantic Meridional Overturning Circulation (AMOC) slowdown beyond the North Atlantic realm. A Peqi'in Cave (Israel) speleothem dated to the last interglacial period (LIG), 129-116 thousand years ago (ka), together with a large modern rainfall monitoring dataset, serve as the base for investigating past AMOC slowdown effects on the Eastern Mediterranean. Here, we reconstruct LIG temperatures and rainfall source using organic proxies (TEX86) and fluid inclusion water d-excess. The TEX86 data show a stepwise cooling from 19.8 ± 0.2° (ca. 128-126 ka) to 16.5 ± 0.6 °C (ca. 124-123 ka), while d-excess values decrease abruptly (ca. 126 ka). The d-excess shift suggests that rainfall was derived from more zonal Mediterranean air flow during the weakened AMOC interval. Decreasing rainfall d-excess trends over the last 25 years raise the question whether similar atmospheric circulation changes are also occurring today.
... Early studies of cyclone identification were mainly based on synoptic charts or satellite images (Taljaard 1965(Taljaard ,1967Streten and Troup 1973;Carleton 1979) and the results vary among different observers. Thanks to a variety of objective tracking algorithms developed since the 1990s (Alpert et al. 1990;Murray and Simmonds 1991;König et al. 1993;Hodges 1994;Serreze et al. 1995;Blender et al. 1997;Sinclair 1997;Hewson et al. 1997;Schubert et al. 1998;Flaounas 2014), the time-consuming and subjective manual identification of synoptic charts has gradually been eliminated (Murray and Simmonds 1991). Objective cyclone tracking algorithms have been widely used in the identification and tracking of cyclones in the northern and southern hemispheres (Jones and Simmonds 1993;Ueno 1993;Haak and Ulbrich 1996;Hodges 2002, 2005;Wei and Qin 2016;Bauer et al. 2016). ...
The ERA5 new generation of high-resolution reanalysis provides a possibility to obtain more accurate cyclone tracks in the Southern Ocean. With a commonly used cyclone tracking algorithm, this study evaluates the impact of data resolution on Southern Ocean cyclone tracks for the period from 1980 to 2020 by preprocessing the ERA5 dataset at different spatial and temporal resolutions. A new track-matching method is proposed to assure an accurate comparison of different track datasets, considering the multiple match pairs and best match pair for each track. It is found that the number, distribution, and characteristics of cyclones are considerably different for various resolution scenarios. The higher spatial resolution captures more tracks, while the increased temporal resolution decreases the number, as well as the lifetime and the moving distance of tracks. The shared cyclones of different track datasets show different characteristics, influenced by both spatial and temporal resolutions. Higher spatial resolution schemes tend to identify more additional track points after the overlapping time of shared tracks rather than before. The spatial distribution pattern of additional track points is consistent when increasing temporal or spatial resolution separately. These results are a reference for the application of objective tracking algorithms in the Southern Ocean using input data with higher resolution.
Significance Statement
Automatic tracking algorithms are important tools for the research of cyclones and their associated weather phenomena. High-resolution input data are available now for cyclone tracking but it also brings more noise that may affect the results. The problem can be solved by a preprocess (smoothing) process using suitable spatial and temporal resolutions. This study compared the features of Southern Ocean cyclones obtained by different spatial and temporal resolution schemes. We further study the shared cyclones in different track datasets with a new track-matching method and discuss the different impacts of spatial and temporal resolution, as well as provide a reference for the application and improvement of cyclone tracking in the future.
... Northern and western African areas have dust emission associated to depressions of up to 80%. In most North African regions, their contributions to dust emission during winter reach values of around 50% (Alpert et al., 1990). Larger fluxes, however, are associated to depressions in West Sahara, Libya, Tunisia, and Sudan with values exceeding 80% (Thorncroft and Hodges, 2000). ...
The study of daily and hourly average concentrations variability of surface O3, NO, NO2 and PM10 was carried out at the proximity of a crossroad (23,000 vehicles per day) located in suburban Gabes, Tunisia. It was performed during 2017-2019 "winter/spring" seasonal transitions and spring seasons. Depending on multi-scale sources and meteorology, it showed variable values within each studied annual period and the years. Statistical approaches based on factorial analysis of correspondences (FAC) and principal component analysis (PCA) revealed three main components of pollution; local retraced by NOx, regional by O3 and synoptic by PM10. Furthermore, they have refined the significant impacts of Saharan dust advections on high recorded PM10 and NOx (by drained urban plume) and of both deep depressions (cut-off lows) and Azores anticyclonic events on the excess of surface O3 concentrations. The investigation of the air quality health index (AQHI) related to the selected pollutants highlighted the significant effect of PM10. It has revealed that more than 53% of the total days were retraced by a moderate air quality index level linked to the negative impact of PM10. Besides, for such a pollutant, more than 20% of the total days were unhealthy for sensitive groups. Even for ordinary people, almost 3% of the total days were shown to be very unhealthy to hazardous.
... They pointed out that 3/5 of the storm events between 2003 -2011 hit Antalya. Various researchers investigated the spatial pattern of cyclones over the Mediterranean (Alpert et al., 1990;Lionello et al., 2016), and Antalya Bay has a high cyclone track density. Potential changes in frequency/intensity of medicanes would increase the physical damage risk on the buildings. ...
HAVE WE VALUED OUR CITIES ENOUGH?
Values bind us together which makes our communities stronger and united. Communities are built upon our tolerance and understanding of the value of our ties, and ties pave our cities towards a bright future. The structure of this book is constructed around the concept of “value”. It contains a collection of readings about the Challenges we face in Cities, Culture, and Heritage. The book is divided into three Parts. The first part focuses on aesthetical values; the second contains articles on cultural values in cities, and the third part is a specialized theme on water values and urban areas. Collectively, the 12 chapters discusses findings, approaches, methodologies, and provide new ways of understanding values in old and new cities. This collection of essays and contributors is concerned with underlying issues such as architectural values, heritage and the city, urban identity, conservation and preservation, water values, and climate issues. Each part contains several chapters to enable cross-reference and comparison. This book is a useful collection of academic resource which discusses some questions and issues that cities have to face.
... They pointed out that 3/5 of the storm events between 2003 -2011 hit Antalya. Various researchers investigated the spatial pattern of cyclones over the Mediterranean (Alpert et al., 1990;Lionello et al., 2016), and Antalya Bay has a high cyclone track density. ...
Values bind us together which makes our communities stronger and united. Communities are built upon our tolerance and understanding of the value of our ties, and ties pave our cities towards a bright future. The structure of this book is constructed around the concept of value”. It contains a collection of readings about the Challenges we face in Cities, Culture, and Heritage. The book is divided into three Parts. The first part focuses on aesthetical values; the second contains articles on cultural values in cities, and the third part is a specialized theme on water values and urban areas. Collectively, the 12 chapters discusses findings, approaches, methodologies, and provide new ways of understanding values in old and new cities. This collection of essays and contributors is concerned with underlying issues such as architectural values, heritage and the city, urban identity, conservation and preservation, water values, and climate issues. Each part contains several chapters to enable cross-reference and comparison. This book is a useful collection of academic resource which discusses some questions and issues that cities have to face.
... They pointed out that 3/5 of the storm events between 2003 -2011 hit Antalya. Various researchers investigated the spatial pattern of cyclones over the Mediterranean (Alpert et al., 1990;Lionello et al., 2016), and Antalya Bay has a high cyclone track density. Potential changes in frequency/intensity of medicanes would increase the physical damage risk on the buildings. ...
A Humble beginning: the Agricultural Heritage of Marano di Napoli behind the Familiar aspects of the Nasti’s rising entrepreneurial framework; The suburb of Marano town was not yet acquainted with its archaeological rich�es which have nevertheless been modestly valued over recent time.
The 19th century rhythm was marked by the Piedimonte Alifana railway (Carac�ciolo, G.) and Belgian Societé Anonyme de Tramways du Nord de Naples tramway network (Bevere, E. et al., 1998) that accompanied its dynamism together with the metallic noises from the workshops operating night and day in a piecework regime.
The peasant life of the hills of Marano of Napoli, as historically document�ed for the small-scale and parochial bourgeoisie, was regulated until the mid-twentieth century by the production of cherries, currently a recognized product, and on the consequent cleaning of the branches of these trees carefully chosen for the making the baskets. The malleability of these woods is due to the historical selection of the arecca cultivar, of which the hill where it rises, from the Spanish lands by the hand of Princess Cartina
Manriquez.
Until the first half of the last century, a multitude of mules shuttled between the Arecca hill and the processing areas, where dozens of workers combined the rectangular boxes also called varriate. The trees were up to twenty meters high and required a long and narrow staircase called scalillo with a special indentation on which the collector rested his knee in such a way as to be free in the use of both hands during the gathering.
... These rainy events are often associated with a cyclone at surface level and a trough or cut-off low at upper levels, transporting cold air masses from the north over the warm Mediterranean Sea (Alpert & Reisin, 1986;Shay-El & Alpert, 1991). Since the climatological footprint of these cyclones is found over Cyprus, they are regularly termed 'Cyprus Lows' (Alpert, et al., 1990). Alike other Mediterranean cyclones, the frequency and associated rainfall of Cyprus Lows has been projected to decline in the 21 st century, while their wind intensity has been projected to increase, although with a higher degree of uncertainty (Hochman, et al., 2018;Reale, et al., 2021). ...
Proxy-based hydro-climatic reconstructions over the Levant suggest enhanced water availability during the Last Glacial Maximum (LGM) compared to present-day conditions. To date, the governing hypothesis is that additional water availability may be directly linked to increased Cyprus Low frequency and intensity over the region. However, this paradigm has not been tested in a modelling framework. With this aim, we analyzed results from a weather type classification algorithm and regional climate simulations. The weather type classification is applied to ERA5 Reanalysis data for present-day (1979-2018) and two PMIP3/PMIP4 pre-industrial and LGM model runs. Dynamical downscaling of the two models with the regional WRF model shows that the present hydro-climate can largely be reproduced. Our simulations suggest that both evaporation and precipitation were lower in the LGM compared to pre-industrial conditions, and that their relative changes can thus most likely explain the additional water availability during that time. Indeed, evaporation in the eastern Mediterranean is reduced to a higher degree (~-33%) as compared to precipitation (~-20%) during the LGM. Particularly, lower evaporation during LGM summer may have sustained the year-round wetter conditions in the Levant. In addition, we find significant changes in Cyprus Low characteristics for the LGM. The simulated daily precipitation associated with Cyprus Lows is significantly lower than pre-industrial values (reduction of 26 - 29%), whereas the wind intensity is stronger (increase of 7 - 8%). Finally, a significant increase in Cyprus Low frequency during LGM winter is likely (+22%). Indeed, our findings are in line with a plethora of proxy-based reconstructions, and provide a reinterpretation of the driving mechanism of water availability, i.e., strong changes in evaporation rather than precipitation. This study places projected hydro-climatic drying of the Levant in a long timescale perspective. As such, it improves our understanding of the physical processes influencing the hydrological cycle in this vulnerable region, situated on the border between sub-tropical and mid-latitude climatic zones.
... The most active cyclogenesis areas over the Mediterranean region, according to [3][4][5][6], are located mostly along the northern coast in winter (e.g., the Gulf of Genoa/Ligurian Sea, Aegean Sea, Black Sea, Balearic Sea, Gulf of Lyon, Adriatic Sea, Ionic Sea, Crete) and along the southern, western, and eastern coasts in summer (e.g., Iberian Peninsula, the southern slopes of the Atlas Mountains, Gulf of Gabes, Gulf of Sidra, Cyprus). Explosive cyclones tend to form in the Western Mediterranean, though their scale and depth is greater in the Eastern Mediterranean [7]. ...
Our understanding of the time variability of intense cyclones in the Mediterranean region is still lacking despite its importance for the long-term forecast of climate anomalies. This study examines the month-to-month variability and predictability of cyclones, the intensity of which exceeded the 75th percentile (intense cyclones) and the 95th percentile (extreme cyclones), over the Western and Eastern Mediterranean. The locations of cyclones were obtained by applying the method of M. Yu. Bardin on the 6-hourly 1000 hPa geopotential height data from the NCEP/NCAR reanalysis for the period 1951–2017 (67 years). It was shown that annual frequencies of cyclones were higher in the Western Mediterranean due to the contribution of spring and autumn; monthly averages were higher in the Eastern Mediterranean in December/January–March for intense/extreme cyclones. In the context of global warming, no linear trends significant at the 90% confidence level were found in the variability of intense and extreme cyclones, except for a positive trend in autumn extreme cyclones over the Eastern Mediterranean. The time series of cyclones in both parts of the Mediterranean were characterized by a pronounced interannual variability with a noticeable decadal modulation. According to spectral analysis, these interannual periods were multiples of 2–3 years corresponding to the main global teleconnection patterns. Seasonally, the most energy was concentrated in winter spectra; spring and autumn spectra had lower comparable magnitudes. The correlation analysis between the frequency of cyclones and the indices of the main atmospheric patterns showed that the main synchronous patterns for intense and extreme Mediterranean cyclones in September–April were the Mediterranean Oscillation (with the opposite signs for the Western and Eastern Mediterranean), Scandinavia pattern (positive correlation), and East Atlantic Oscillation (negative correlation). Additional important synchronous teleconnection patterns for some months were the Arctic Oscillation and East Atlantic/West Russia pattern for the Western Mediterranean, and the Polar/Eurasia pattern and Tropical Northern Hemisphere pattern for the Eastern Mediterranean. The outcome of this paper was the use of an artificial neural network model with inputs of global teleconnection indices both in the atmosphere and ocean to describe the temporal variability of the frequency of intense cyclones in the Western and Eastern Mediterranean. The predictability of intense cyclones was shown with the possibility of forecasts with a lead time of 0, 2, 4, and 6 months for the Western Mediterranean in October, January, February, April, and May, and for the Eastern Mediterranean in January, February, March, April, and May. One of the applications of this model may be in forecasting the evolution of the monthly frequency of cyclones with a lead time of 2 to 6 months.
... The first objective method for Mediterranean cyclones was introduced by Alpert et al. (1990). They used the ECMWF based on monthly data of a 5-year period (1982)(1983)(1984)(1985)(1986)(1987) to analyze the cyclone frequencies plus cyclonic tracks with a shorten temporal and spatial resolution (12-h temporal resolution and 2.5 • spatial resolution). ...
The purpose of this study is to analyze the dynamic effect of Sudan Low on the precipitation in Iran. In this study, the up level data (i.e., data from 600, 700, and 1000 hPa levels) were taken from NCEP/NCAR and ECMWF websites in a 32-year period (from 1999 to 2020). In order to investigate dynamic and thermodynamic characteristics of Sudan Low, the data of geopotential height (Hgt), sea level pressure (SLP), omega, and wind flow (UWnd, VWnd), mean daily precipitation and temperature, and monthly northward surface stream were exploited at the fore mentioned levels. The findings showed that the potential of air and moisture passage of Sudan Low over Iran in 1999, 2006, and 2011 had the most progression compared to the normal condition, and this progression reached to 42° northern latitude. In other finding, it was observed that the northward surface stream during December, January, and February in the 32-year period caused the most appropriate precipitation in Iran, and the Arabian Sea along with the Bab-el-Mandeb was the generator of this situation. Along with the above finding, it was found that jet stream creates atmospheric rivers that originate in Africa and is reinforced by Sudan Low, transferring moisture to the upper atmosphere levels of Iran. Between the positive and negative omega contours of about 600 hPa, high precipitation for Iran was caused. Finally, the overall results indicated that in order to complete the investigation of Sudan Low effects on Iran’s precipitation, the atmospheric river of 26 March 2019 was observed. The result showed that the amount of precipitation originating from this atmospheric river which is reinforced by the Arabian Sea and Mediterranean Sea had a broad impact on Iran’s precipitation.
... Rain events in semiarid and arid subtropical regions are characterized by a high rate of interannual variability ( L o c k w o o d 1 9 8 8 ) a n d o c c u r a s a r e s u l t o f tropical-extratropical interactions (Ziv 2001;Knippertz 2005;Ziv et al. 2005;De Vries et al. 2013;Martius et al. 2013). Furthermore, regional cyclogenesis and cyclone tracks influence the Mediterranean and produce favorable rainfall conditions (Alpert et al. 1990;Flocas and Giles 1991;Trigo et al. 1999;Maheras et al. 2001) that are strongly related to the prevailing circulation regime. ...
Surface observations of rain from 15 stations across the northern Arabian Peninsula (AP) and meteorological data from the NCEP/NCAR reanalysis data set were used to study the winter atmospheric factors and subtropical jet stream (STJ) characteristics controlling rain over the northern AP. The statistical study shows that January has the highest amount of winter rain when the STJ is at 200 hPa and is located in the zone between 25°N and 30°N. Synoptically, the northern AP winter rain forms when the Red Sea trough (RST) extends northward and is located to the east of the upper trough, while the rain decreases when the Siberian high intensifies, the pressure gradient around the RST decreases and the STJ becomes zonal or exits over the Middle East. Moreover, the study shows that the Mediterranean cyclone plays a secondary role in the generated rain, mainly producing atmospheric conditions favoring the northward extension of the RST. The results demonstrate that the pressure/geopotential gradient is more important than the relative positions of atmospheric systems in the development of rain. The temporal and vertical variations in the STJ indicate that the rain decreases as the core of the low-pressure difference shifts southward from the northern Red Sea. Additionally, the amount of the Siberian high difference is comparable to the negative low-pressure difference, while the Azores difference is relatively weak.
... The majority of dust storms over the eastern Mediterranean basin occur between December and April with maximum dust load during April (Israelevich et al., 2002). The main zones of cyclogenesis in the Mediterranean Sea determine dust uplift and transport in the region (Alpert et al., 1990;Bou Karam et al., 2010). Heavy dust periods over the eastern Mediterranean are frequently associated with the so-called Cyprus Low (Katsnelson, 1970;Dayan et al., 2008) as well as the Sharav cyclone (Alpert and Ziv, 1989), which transport dust from the Arabian deserts and northern Sahara into the eastern Mediterranean basin where they are frequently observed over Cyprus. ...
This paper presents measurements of mineral dust concentration in the diameter range from 0.4 to 14.0 µm with a novel balloon-borne optical particle counter, the Universal Cloud and Aerosol Sounding System (UCASS). The balloon launches were coordinated with ground-based active and passive remote-sensing observations and airborne in situ measurements with a research aircraft during a Saharan dust outbreak over Cyprus from 20 to 23 April 2017. The aerosol optical depth at 500 nm reached values up to 0.5 during that event over Cyprus, and particle number concentrations were as high as 50 cm −3 for the diameter range between 0.8 and 13.9 µm. Comparisons of the total particle number concentration and the particle size distribution from two cases of balloon-borne measurements with aircraft observations show reasonable agreement in magnitude and shape despite slight mismatches in time and space. While column-integrated size distributions from balloon-borne measurements and ground-based remote sensing show similar coarse-mode peak concentrations and diameters, they illustrate the ambiguity related to the missing vertical information in passive sun pho-tometer observations. Extinction coefficient inferred from the balloon-borne measurements agrees with those derived from coinciding Raman lidar observations at height levels with particle number concentrations smaller than 10 cm −3 for the diameter range from 0.8 to 13.9 µm. An overestimation of the UCASS-derived extinction coefficient of a factor of 2 compared to the lidar measurement was found for layers with particle number concentrations that exceed 25 cm −3 , i.e. in the centre of the dust plume where particle concentrations were highest. This is likely the result of a variation in the refractive index and the shape and size dependency of the extinction efficiency of dust particles along the UCASS measurements. In the future, profile measurements of the particle number concentration and particle size distribution with the UCASS could provide a valuable addition to the measurement capabilities generally used in field experiments that are focussed on the observation of coarse aerosols and clouds.
... The Browning and Goodwin (2013; approach uses the average pressure gradient to decide on the existence of a cyclone and to indicate the intensity of the cyclone, similar to Alpert (1990), this approach is referred to as the pressure gradient (PG) method. In the PG method, closed low pressure systems are identified from un-interpolated sea level pressure fields within the region shown in Figure 1. ...
East Coast Lows (ECLs) are important weather systems that affect the eastern seaboard of Australia. They have attracted research interest for both their destructive nature and water supplying capability. In this paper, three objective ECL tracking methods are applied to the twentieth century reanalysis ensemble (20CRV2C) for the period of 1851–2014 to identify historical trends and variability in ECLs. While the ensemble mean is unsuitable for tracking ECLs, when all methods are applied to the full 56-member ensemble there is large agreement between tracking methods as to the low-frequency variability and trends in ECLs. The uncertainty between 56 ensemble members has dramatically decreased in recent decades. For comparison, the three tracking methods are also applied to ERA-I reanalysis dataset for the overlapping time period (1980-2009). The inter-annual variability and monthly distribution of ECLs agrees well between different reanalysis for each of tracking methods. The most recent decade has had relatively low numbers of ECLs compared to the previous century.
... The majority of dust storms over 35 the eastern Mediterranean basin occurs between December and April with maximum dust load during April (Israelevich et al., 2002). The main zones of cyclogenesis in the Mediterranean Sea determine dust uplift and transport in the region (Alpert et al., 1990). Heavy dust periods over the eastern Mediterranean are frequently associated with the so-called Cyprus Low (Katsnelson, 1970;Dayan et al., 2008) as well as the Sharav cyclone (Alpert and Ziv, 1989) which transport dust from the Arabian deserts and northern Sahara into the eastern Mediterranean basin where they are frequently observed over Cyprus. ...
This paper presents measurements of mineral dust concentration in the diameter range from 0.4 to 14.0 µm with a novel balloon-borne optical particle counter, the Universal Cloud and Aerosol Sounding System (UCASS). The balloon launches were coordinated with ground-based active and passive remote-sensing observations and airborne in-situ measurements with a research aircraft during a Saharan dust outbreak over Cyprus from 20 to 23 April 2017. The aerosol optical depth at 500 nm reached values up to 0.5 during that event over Cyprus and particle number concentrations were as high as 50 cm −3 5 for the diameter range between 0.8 and 13.9 µm. Comparisons of the total particle number concentration and the particle size distribution from two cases of balloon-borne measurements with aircraft observations show reasonable agreement in magnitude and shape despite slight mismatches in time and space. While column-integrated size distributions from balloon-borne measurements and ground-based remote sensing show similar coarse-mode peak concentrations and diameters, they illustrate the ambiguity related to the missing vertical information in passive sun photometer observations. Extinction coefficient inferred 10 from the balloon-borne measurements agrees with those derived from coinciding Raman lidar observations at height levels with particle number concentrations smaller than 10 cm −3 for the diameter range from 0.8 to 13.9 µm. An overestimation of the extinction coefficient of a factor of two was found for layers with particle number concentrations that exceed 25 cm −3. This is likely the result of a variation in the refractive index, the shape-and size-dependency of the extinction efficiency of dust particles along the UCASS measurements.
... Detailed description of these cyclones can be found in P. Khain, et al. Atmospheric Research 247 (2021) 105213 Sharon and Kutiel, 1986;Alpert et al., 1990;Shay-El and Alpert, 1991;Ziv et al., 2006. Fig. 5 presents the initial (left panels) and the decay (right panels) stages of the cyclone evolution over the EM. ...
Numerical Weather Prediction (NWP) models with coarser resolution than ~4 km use convection parametrization to describe both deep and shallow convection. Convection permitting models with grid spacing below ~4 km usually describe deep convection on grid scale, but still parametrize the shallow convection, being sub-grid scale process. Many of these parametrizations are based on the mass-flux approach. The artificial combination of resolved and parametrized convection might deteriorate the model forecast skill, particularly precipitation. In this study, we are using the COSMO 2.5 km resolution limited area NWP model over the Eastern Mediterranean region to analyze the effect of the mass-flux shallow convection parametrization (SCP) on the forecasts skill. We show that SCP entrainment rate, as well as restrictions on the shallow convection development height and maximum updraft speed, have a crucial effect on the forecasts of precipitation, temperature and moisture. Physically motivated tuning of these parameters can improve the model forecasts significantly. Finally, we estimate the climatic zones and seasons where SCP is expected to be particularly important for NWP.
... Cyprus Lows are mid-latitude low-pressure systems that tend to develop over the Eastern Mediterranean (Fig. 1). They are associated with cool air transport over the region, typically originating from Eastern Europe, over the warmer Mediterranean Sea where it becomes moist and unstable (Alpert et al., 1990). This air is transported towards Israel, the Palestinian Authority and Jordan, leading to wet conditions and low temperatures (Fig. 1). ...
The prediction of the occurrence of infectious diseases is of crucial importance for public health, as clearly seen in the ongoing COVID-19 pandemic. Here, we analyze the relationship between the occurrence of a winter low-pressure weather regime - Cyprus Lows - and the seasonal Influenza in the Eastern Mediterranean. We find that the weekly occurrence of Cyprus Lows is significantly correlated with clinical seasonal Influenza in Israel in recent years (R = 0.91; p < .05). This result remains robust when considering a complementary analysis based on Google Trends data for Israel, the Palestinian Authority and Jordan. The weekly occurrence of Cyprus Lows precedes the onset and maximum of Influenza occurrence by about one to two weeks (R = 0.88; p < .05 for the maximum occurrence), and closely follows their timing in eight out of ten years (2008–2017). Since weather regimes such as Cyprus Lows are more robustly predicted in weather and climate models than individual climate variables, we conclude that the weather regime approach can be used to develop tools for estimating the compatibility of the transmission environment for Influenza occurrence in a warming world. Furthermore, this approach may be applied to other regions and climate sensitive diseases. This study is a new cross-border inter-disciplinary regional collaboration for appropriate adaptation to climate change in the Eastern Mediterranean.
... À grande échelle, il est influencé par la NAO (North Atlantic Oscillation) qui, en phase positive, entraîne les dépressions sur le nord de l'Europe et par conséquent un climat froid et sec sur les côtes méditerranéennes tandis que la phase négative de la NAO se traduit par un climat plus chaud et plus humide autour de la Méditerranée (Ulbrich et al., 1999;Xoplaki et al., 2003). Le climat sur cette région est aussi influencé par les dépressions venues de l'océan Atlantique qui sont à l'origine d'une grande part des précipitations de l'automne au printemps (Alpert et al., 1990;Maheras et al., 2001). À plus fine échelle, le relief autour de la Méditerranée joue un rôle important sur le climat du bassin méditerranéen car il est générateur de forts vents régionaux. ...
La région Euro-méditerranéenne est soumise à de fortes charges en aérosols d’origine variée et présentant une forte variabilité spatio-temporelle. Le climat de cette région va en être impacté suite à leur effet direct sur le rayonnement mais aussi à travers leurs effets semi-direct et indirects sur les nuages et la dynamique atmosphérique. Ces travaux de thèse, s’inscrivant dans les programmes de recherche Med-CORDEX et ChArMEx, vont aborder au travers de la modélisation climatique régionale la question de l’impact radiatif direct des différents aérosols sur la période historique, leur évolution entre la période 1971-2000 et la période 2021-2050 ainsi que celle de la sensibilité du climat futur de cette région à ces aérosols. Afin d’avoir une prise en compte la plus complète possible des aérosols anthropiques dans le modèle climatique régional ALADIN-Climat, utilisé tout au long de ce travail de thèse, un nouveau module d’aérosols simplifié permettant de représenter les particules de nitrate et d’ammonium a été implémenté dans son schéma interactif d’aérosols TACTIC. Un ensemble de simulations, prenant en compte ou non les particules de nitrate et d’ammonium, a été réalisé sur la période 1979-2016. Les résultats ont montré l’impact important de ces particules atmosphériques sur le climat de la région Euro-Méditerranéenne avec une contribution à hauteur de 40% à l’AOD totale (à 550 nm) ainsi qu’un forçage radiatif direct supérieur à celui des particules de sulfate et de carbone organique à partir de l’année 2005. Sur une période de temps plus longue et en utilisant différents scénarios, les résultats montrent une baisse de 35% de l’AOD totale sur l’Europe entre les périodes 1971-2000 et 2021-2050. Celle-ci est principalement due à la forte diminution de l’AOD des aérosols de sulfate compensée en partie par la hausse des nitrates. Ces derniers auront par ailleurs la contribution à l’AOD totale la plus élevée sur l’Europe, à hauteur de 45%, sur la période future. Cette évolution des différents aérosols va impacter leur forçage radiatif direct avec notamment une baisse significative de celui exercé par les particules de sulfate et une hausse de celui des aérosols de nitrate et d’ammonium. Ces changements, robustes en fonction des différents scénarios, expliquent en moyenne annuelle environ 6% du réchauffement climatique attendu sur l’Europe entre les deux périodes, principalement dû aux interactions aérosols-rayonnement mais également par une modification de l’albédo des nuages (premier effet indirect) et de la dynamique atmosphérique sur cette région.
... Many satellite-borne sensors have been used for dust storm detection because of their superiorities, such as the high spectral resolution and broad field of view. Moderate Resolution Imaging Spectroradiometer (MODIS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), Chinese Feng Yun series (FY), Advanced Very High Resolution Radiometer (AVHRR), Ozone Monitoring Instrument (OMI), Total Ozone Mapping Spectrometer (TOMS), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Spinning Enhanced Visible and Infrared Imager (SEVIRI), sea-Viewing Wide Field-of-view Sensor (SeaWIFS), Polarization and Directionality of the Earth's Reflectances (POLDER), Medium Resolution Imaging Spectrometer (MERIS), Earth Polychromatic Imaging Camera (EPIC), and National Polar Orbiting Partnership Visible infrared Imaging Radiometer (NPP VIIRS) have provided considerable information about the properties of objects used for dust detection (Abe et al., 2005;Adushkin et al., 2018;Ahn et al., 2008;Alizadeh-Choobari et al., 2014;Alpert et al., 2004Alpert et al., , 1990Alpert and Ganor, 2001;Ambaum et al., 2001;Amyotte and Eckhoff, 2010;Andrews et al., 2010;Ashpole and Washington, 2013;Yang and Ren, 2017). Most of those are polar-orbiting satellites, which have higher spatial resolution and more channels with wider spectral range compared with the geostationary satellites. ...
Enhancing the dust storm detection is a key part for the environmental protection, human healthy and economic development. The goal of this paper is to propose a new Support Vector Machine (SVM)-based method to automatically detect dust storms using remote sensing data. Existing methods dealing with this problem are usually threshold-based that are of great complexity and uncertainty. In this paper we propose a simple and reliable method combining SVM with MODIS L1 data and explore the optimal band combinations used as the feature vectors of SVM. The developed method was evaluated by MODIS and OMI data qualitatively and quantitatively on three study sites located in the Arabian Desert, Gobi Desert and Taklimakan Desert, and it was also compared to three other traditional methods based on their accuracy, complexity, reliability and sensitivity to thresholds. The detection results demonstrated that the combination of (Band7 − Band3)/(Band7 + Band3) ((B7 − B3)/(B7 + B3)), Band20 − Band31 (B20 − B31), and Band31/Band32 (B31/B32) can detect the dust storms more precisely than other individual bands or their combination. The comparison among those cases indicated that the proposed automatic method exhibited an advantage of minimizing the uncertainty and complexity, which were the limits of defining thresholds based on the threshold-based methods. The conclusions can provide references for studies that focus on statistical-based dust storm detection.
... In summary, the sea surface under warming and the cyclogenetic character of the gulfs of Lion and Genoa (Alpert et al., 1990;Jansà et al., 2001) could account for the temporal behavior of type A and of CYC, opposite to those found by other authors at larger scales or in other parts of the Mediterranean basin, for periods somewhat different to those analyzed herein. ...
We determined the weather type, according to the Jenkinson and Collison procedure, of the 22 646 days in the 1948-2009 period for the western Mediterranean basin. The analysis is based upon the surface pressure values of the NCEP/NCAR reanalysis, for a grid of nine points with extreme vertices at 45º N, 5º W and 35º N, 15º E, which provides a broad synoptic catalogue for this region. We analyzed the trends of the types and their different groupings during the same period. The most frequent type is U (undetermined), with an annual average of approximately 100 days (99.4, 27.2%), followed by type A (anticyclone), with 75.5 days/ year (20.7%), and C (depression), with 67.8 days/year (18.6%). The high frequency of type U is due to the habitual pressure of baric fields with a low gradient over Mediterranean waters in the warm half of the year. According to their directions, the types from the west are the most frequent and those from the south, the least. The monthly regime of the most frequent types and groupings is quite regular; type C groups, as well as advective and cyclonic curvature groups, present summertime minima and maxima in the cold half of the year, whereas the opposite occurs with types U and A. The main statistically significant annual trends in the 1948-2009 period involve a decrease in type A (–4.19 days/decade, that is, –29.0%) and an increase in type U, the cyclonic types and those presenting an easterly component. On comparing the 31-yr sub-pe- riods 1948-1978 and 1979-2009, the tendencies of A and U were confirmed, and increases can generally be seen in the types presenting an easterly component and a decrease in those with a westerly component. The variation in type A ranged from 2490 days in the first sub-period to 2192 in the second one (p = 0.000), mainly concentrated in summer and autumn. This evident reduction of type A coincides, paradoxically, with an increase in the sea surface pressure variable (+0.31 hPa/decade) throughout the 62 years of analysis. The negative trend found in type A differs from the results of some studies. The different analysis periods, the different scales or areas of study and the variety of methods used to determine the weather types can account for the fact that these results are discordant. Moreover, warming over the last few decades in the waters of the western Mediterranean basin, as well as the clearly cyclogenetic character of the gulfs of Lion and Genoa, might account for the decrease in type A and the increase in the cyclonic curvature types.
... The region's climate is intensely affected by external forcing of both mid-latitude and tropical origins (e.g., Alpert et al., 2005). However, the rain in the Mediterranean part of Israel results mainly from passage or development of extratropical cyclones over the eastern Mediterranean, known as the Cyprus Lows (HMSO, 1962;Sharon and Kutiel, 1986;Alpert et al., 1990;Shay-El and Alpert, 1991;Trigo et al., 1999;Schädler and Sasse, 2006;Ziv et al., 2006Ziv et al., , 2015. Saaroni et al. (2010a) found that the average contribution of Cyprus Lows to the rainfall in Israel is 83%. ...
Global climate models provide only partial information on local‐scale phenomenon, such as precipitation, primarily due to their coarse resolution. In this study, statistical downscaling algorithms, based on both weather regimes and past analogues, are operated for 18 Israeli rain gauges with an altitude ranging between −200 and ~1,000 m above sea level (ASL). To project seasonal precipitation over Israel and its hydrologic basins, the algorithms are applied to six Coupled Model Inter‐comparison Project Phase 5 (CMIP5) models for the end of the 21st century, according to the RCP4.5 and RCP8.5 scenarios. The downscaled models can capture quite well the seasonal precipitation distribution, though with underestimation in winter and overestimation in spring. All models display a significant reduction of seasonal precipitation for the 21st century according to both scenarios. The winter reductions for the end of the century and the RCP8.5 scenario are found to be ~22 and ~37% according to the weather regimes and the analogues downscaling methods, respectively. Spring reductions are found to be ~10–20% larger than winter reductions. It is shown that the projected reduction results from a decrease in the frequency of the rain‐bearing systems, as well as a decrease in the average daily precipitation intensity. The areas with the largest reductions in seasonal precipitation are found over the central mountains, the Mediterranean coastal area, and the Sea of Galilee hydrologic basins, which are the main fresh‐water aquifers and reservoirs of Israel. The statistical downscaling methods applied in this study can be easily transferred to other regions where long‐term data sets of observed precipitation are available. This study and others may serve as a basis for priority and policy setting toward better climate adaptation with associated uncertainties related to the methods used and nonstationary of the climate system.
... The synoptic-scale systems affecting the EM that are responsible for most of the annual rainfall are the extratropical cyclones: the "Cyprus Lows" (Sharon and Kutiel, 1986;Alpert et al., 1990;Ziv et al., 2006). The rain is formed within cold air masses of European origin that enter the region from the northwest. ...
In lack of convection‐permitting numerical weather prediction (NWP) ensembles, the most recent deterministic NWP precipitation forecast is usually addressed. However, the exact intensity, location, and timing of a deterministic precipitation forecast is not always reliable because of the chaotic nature and complexity of precipitation formation mechanisms. This study examines a way to optimize the utilization of precipitation forecasts of deterministic NWP models. More specifically, the study suggests utilizing a spatially smoothed time‐lagged ensemble (TLE) to obtain more reliable precipitation forecasts. A global numerical weather prediction model (IFS) and a regional convection‐permitting NWP model (COSMO) over the Eastern Mediterranean during 2016‐2018 are used for analysis. First, we define light, light‐moderate, and moderate intensities for 6‐hourly accumulated precipitation (6hAP) and investigate the corresponding definitions for 1‐hourly accumulated precipitation (1hAP). Next, Fractional Skill Score (FSS) is used to estimate the optimal spatial smoothing scale of a deterministic precipitation forecast for the three intensity categories for 6hAP and 1hAP. FSS is also used to compare COSMO and IFS deterministic precipitation forecasts, and to analyze the skill degradation with the forecast range. It is quantitatively shown that the useful scale of precipitation forecasts is smaller for larger accumulation time intervals. Finally, precipitation forecast of TLE are formed from successive smoothed deterministic forecasts, and compared with the most recent deterministic forecast. It is found that on average, TLEs have better skills both for 6hAP and 1hAP. The reason for this improvement in skill is illustrated using a case study as an example. This article is protected by copyright. All rights reserved.
... Mean annual precipitation (climatological mean, last 30 years) in the Levant displays a steep gradient, from hyper-arid in the south with less than 100 mm/y (e.g., Egypt, Southern Negev), through semi-arid with 500-600 mm/y (e.g., Soreq, Jerusalem) to humid in the north with >1000 mm (Lebanon and Southeast Turkey) ( Figure 2A,B). Precipitation in the Levant is mainly sourced from eastward moving storm tracks generated inside the Mediterranean region, Cyprus low systems, when cold and dry air from continental Euro-Asia interfaces with the relatively warm Mediterranean Sea (Figure 2A compared to Figure 2B) [87,88]. A smaller fraction of cyclones enter on a southeastern trajectory from the Atlantic crossing the Southern EM Sea ( Figure 2B), but rarely reach all the way to the Levant and FC [89]. ...
The Middle East (ME) spans the transition between a temperate Mediterranean climate in the Levant to hyper-arid sub-tropical deserts in the southern part of the Arabian Peninsula (AP), with the complex alpine topography in the northeast feeding the Euphrates and Tigris rivers which support life in the Southeastern Fertile Crescent (FC). Climate projections predict severe drying in several parts of the ME in response to global warming, making it important to understand the controls of hydro-climate perturbations in the region. Here we discuss 23 ME speleothem stable oxygen isotope (δ18Occ) records from 16 sites from the SISAL_v1 database (Speleothem Isotope Synthesis and Analysis database), which provide a record of past hydro-climatic variability. Sub-millennial changes in ME δ18Occ values primarily indicate changes in past precipitation amounts the result of the main synoptic pattern in the region, specifically Mediterranean cyclones. This pattern is superimposed on change in vapor source δ18O composition. The coherency (or lack thereof) between regional records is reviewed from Pleistocene to present, covering the Last Glacial Maximum (~22 ka), prominent events during deglaciation, and the transition into the Holocene. The available δ18Occ time-series are investigated by binning and normalizing at 25-year and 200-year time windows over the Holocene. Important climatic oscillations in the Holocene are discussed, such as the 8.2 ka, 4.2 ka and 0.7 ka (the Little Ice Age) Before Present events. Common trends in the normalized anomalies are tested against different climate archives. Finally, recommendations for future speleothem-based research in the region are given along with comments on the utility and completeness of the SISAL database.
... Finally, cold NPC air outbreaks are known to play a key role in cyclogenesis over the eastern Mediterranean, and in particular the Cyprus Low, which governs a large portion of rainfall over the Middle East. Tarolli et al. (2012) state that: "… over the Mediterranean climate areas of Israel, high precipitation events and extreme flash floods are mainly associated with the Cyprus Low, …a winter extra-tropical cyclone … system … (Sharon and Kutiel, 1986;Alpert et al., 1990;Krichak et al., 2004;Ziv et al., 2006;Wittenberg et al., 2007;Saaroni et al., 2010). The cold air masses gain moisture … over warmer Mediterranean waters and become conditionally unstable. ...
A repeating pattern of multi-centennial-scale Holocene climate events has been widely (globally) documented, and they were termed Rapid Climate Change (RCC) events. Non-seasalt potassium ion (K ⁺ ) series in Greenland ice cores provide well-constrained timings for the events, and a direct timing relationship has been inferred between these events and the frequency of northerly cold polar/continental air outbreaks over the eastern Mediterranean Sea through gaps in the mountain ranges along the northern margin of the basin. There also appears to be a remarkable timing agreement with major archaeological turnover events in the Aegean/Levantine region. Yet no physically consistent assessment exists for understanding the regional climatic impacts of the events around this critical region. We present a simple 2-dimensional Lagrangian model, which yields a broad suite of physically coherent simulations of the impacts of frequency changes in winter-time northerly air outbreaks over the Aegean/Levantine region. We validate this with existing reconstructions from palaeoclimate proxy data, with emphasis on well-validated sea-surface temperature reconstructions and a highly resolved cave speleothem stable oxygen isotope record from Lebanon. Given that the RCCs were clearly marked by negative sea surface temperature anomalies in the region, we find that the predominant climatic impacts of this winter-time mechanism were “cold and wet,” in contrast with intercalated “warmer and more arid” conditions of non-RCC periods. More specifically, the RCCs are found to be periods of highly variable conditions, with an overall tendency toward cold and wet conditions with potential for flash flooding and for episodic snow-cover at low altitudes, at least in the lower-altitude (lower 1–1.5 km) regions of Crete and the Levant. The modelled winter-anomaly process cannot address underlying longer-term, astronomically forced trends, or the relatively warm and arid anomalies in between RCCs. The latter require further study, for example with respect to potential (summer-time?) extension of evaporative subtropical conditions over the region. Finally, our results imply that the “amount effect” observed in Levantine cave δ ¹⁸ O (and precipitation or drip-water δ ¹⁸ O) may not reflect the conventional concept related to temperature-dependent fractionation and Rayleigh distillation. Instead, it appears to arise from a complex and somewhat counter-intuitive mixing, in shifting proportionalities, between advected (external) and evaporated (Mediterranean) moisture.
... Since 1990 most of the Mediterranean cyclone climatologies (e.g. Alpert et al. 1990), aiming to describe various features of these systems, are based on such techniques and are conducted automatically. The physical and mathematical background of this approach was partly presented in Chervenkov (2014) using the above-mentioned case as a demonstration. ...
We present a study of the Black Sea storms, using a long hindcast of the western Black Sea wind waves. The goal of the work is to study the trends in the storminess indicators. We identify 238 storms with significant wave height above 4 m for the period 1900–2015. We study the cyclogenetic regions of the cyclones causing these storms and focus specifically on the Black Sea storms associated with cyclones originating over the Gulf of Sidra and the adjacent areas. We also identify which of these storms are associated with the so-called explosive cyclogenesis (with deepening rate above 1 Bergeron) and find that 3 out of 5 cases of severe Black Sea storms associated with explosive cyclones are caused by cyclones originating in the Gulf of Sidra. We find no evidence of steady trends in the western Black Sea storminess.
Comment: the article appears twice- once as journal article, second time as a part of topical collection of articles and appears as a book chapter in RG, but the two are identical. Please if You plan to refference it, refference it as a journal article!
... Greece and Turkey (>38ºN) receive cyclones originating to the northwest over central Europe, and in the Gulf of Genoa [80]. The EM coastal areas receive most precipitation from eastward moving storm tracks generated inside the Mediterranean region, Cyprus low systems, when cold and dry air from continental Euro-Asia interfaces with the relatively warm Mediterranean sea [81,82]. A smaller fraction of cyclones enter from outside the Mediterranean region from the Atlantic ( Figure 2B), but rarely reach all the way to the EM and FC. ...
The Middle East spans the transition between temperate Mediterranean climate in the Levant to hyper-arid sub-tropical deserts in the southern part of the Arabian Peninsula, with the complex alpine topography in the northeast feeding the Euphrates and Tigris rivers which support life in the southeastern Fertile Crescent (FC). Climate projections predict severe drying in major parts much of the ME in response to global warming, making it important to understand the controls of hydro-climate perturbations in the region. Here we discuss 23 ME speleothem stable oxygen isotope (δ18Occ) records from 16 sites from the SISAL_v1 database, which provide a record of past hydro-climatic variability. Sub-millennial changes in ME speleothem δ18Occ values primarily indicate changes in past precipitation amounts superimposed on variations of the main synoptic pattern in the region, specifically Mediterranean cyclones. The coherency (or lack thereof) between regional records is reviewed from Pleistocene to present, covering the Last Glacial Maximum (LGM), prominent events during deglaciation, and transition into the Holocene. The available speleothem δ18Occ time-series are investigated by binning and normalizing at 25-year and 200-year time windows over the Holocene. Important Holocene climatic oscillations are discussed, such as the 8.2 ka, 4.2 ka and 0.7 ka (the Little Ice Age) Before Present events. Common trends in the standardized anomalies are tested against different climate archives. Finally, recommendations for future speleothem-based research in the region are given along with comments on the utility and completeness of the SISAL database.
The variation of synoptic systems impacting Iran's precipitation climatology can have significant climatic consequences. Among the cyclones contributing to the occasionally widespread precipitation in Iran are the coincident Mediterranean-Red Sea cyclones (CMRSC). This research aims to elucidate the long-term associated with the frequency and intensity of CMRSC by examining geopotential height (GH) and geopotential height gradient (GHG), along with CMRSC patterns, as influential factors on Iran's precipitation climatology. To achieve this, 4-daily GH data at 1000 hPa from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-Interim, spanning from 1979 through 2018, were utilized. Throughout this period, a total of 97 CMRSC events accompanied precipitation in Iran. Methodologically, the non-parametric Chi-square test, alongside the Standard Normal Homogeneity Test (SNHT), were employed to assess variations in the cyclones' frequency and strength. The Chi-square non-parametric statistic was harnessed to discern trends in GH and GHG, while linear regression was applied to ascertain long-term trends. The findings indicate that the number of CMRSC did not display statistically significant changes over the study period when comparing successive decades and two successive halves of the time series. Notwithstanding, a more detailed examination of shorter timescales, particularly towards the end of the study period, disclosed statistically significant changes in two- and four-year averages. Additionally, the increase in GH at the formation site of Mediterranean cyclones and the decrease in GHG likely contributed to reduced atmospheric instability and precipitation in the affected regions. A pronounced GHG jump in the Mediterranean Sea in 1996 divided the time series into two distinguishable periods. The results demonstrate an upward trend in both periods; however, the second period exhibited a more gradual increase compared to the preceding period.
Between 14.5 and 5 ka, the Sahara was vegetated owing to a wet climate during the African humid period. However, the climatic factors sustaining the “green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD, where D stands for deuterium) of high molecular weight (HMW) n-alkanoic acids in a marine sediment core from the eastern Mediterranean, we provide a continuous record for winter precipitation in the Nile river delta spanning the past 18 kyr. Pairing the data with δD records from HMW n-alkanes from the same core, we show that HMW n-alkanoic acids constantly derived from the delta, while the HMW n-alkanes also received significant contributions from the headwaters between ∼ 15–1 ka when fluvial runoff enhanced. This enables us to reconstruct the evolution of Mediterranean (winter) and monsoonal (summer) rainfall in the Nile river watershed in parallel. In the delta, the Heinrich stadial 1 (HS1) evolved in two phases, with a dry episode between ∼ 17.5–16.0 ka, followed by wet conditions between ∼ 16–14.5 ka. Winter rainfall enhanced substantially between 11–6 ka, lagging behind the intensification of the summer monsoon by ca. 3 kyr. Heavy winter rainfall resulted from a southern position of the Atlantic storm track combined with elevated sea surface temperatures in the eastern Mediterranean, reinforcing local cyclogenesis. We show that during the green Sahara, monsoon precipitation and Mediterranean winter rainfall were both enhanced and infer that the winter rainfall zone extended southwards, delivering moisture to the Sahara. Our findings corroborate recent hypotheses suggesting that winter rains that extended southward were a crucial addition to the northward displacement of the summer monsoon in helping to sustain a green Sahara.
Mediterranean cyclones (MCs) govern extreme weather events across the Euro-African Basin, affecting the lives of hundreds of millions. Despite many studies addressing MCs in the last few decades, their correct simulation and prediction remain a significant challenge to the present day, which may be attributed to the large variability among MCs. Past classifications of MCs are primarily based on geographical and/or seasonal separations; however, here we focus on cyclone genesis and deepening mechanisms. A variety of processes combine to govern MC genesis and evolution, including adiabatic and diabatic processes, topographic influences, land–sea contrasts, and local temperature anomalies. As each process bears a distinct signature on the potential vorticity (PV) field, a PV approach is used to distinguish among different “types” of MCs. Here, a combined cyclone-tracking algorithm is used to detect 3190 Mediterranean cyclone tracks in ECMWF ERA5 from 1979–2020. Cyclone-centered, upper-level isentropic PV structures in the peak time of each cyclone track are classified using a self-organizing map (SOM). The SOM analysis reveals nine classes of Mediterranean cyclones, with distinct Rossby-wave-breaking patterns, discernible in corresponding PV structures. Although classified by upper-level PV structures, each class shows different contributions of lower-tropospheric PV and flow structures down to the surface. Unique cyclone life cycle characteristics, associated hazards (precipitation, winds, and temperature anomalies), and long-term trends, as well as synoptic, thermal, dynamical, seasonal, and geographical features of each cyclone class, indicate dominant processes in their evolution. Among others, the classification reveals the importance of topographically induced Rossby wave breaking to the generation of the most extreme Mediterranean cyclones. These results enhance our understanding of MC predictability by linking the large-scale Rossby wave formations and life cycles to coherent classes of under-predicted cyclone aspects.
Nowadays, several global ensembles (GEs) which consist of several tens of members are being run operationally. In order to locally improve the probabilistic forecasts, various forecasting centers and research institutes utilize the GEs as initial and boundary conditions to drive regional convection permitting ensembles (RCPEs). RCPEs demand significant computer resources and often a limited number of ensemble members is affordable, which is smaller than the size of the driving GE. Since each RCPE member obtains the initial and boundary conditions from a specific GE member, there are many options to select the GE members. The study uses the European Centre for Medium‐Range Weather Forecasts (ECMWF) GE consisting of 50 members, to drive 20 members of COSMO model RCPE over the Eastern Mediterranean. We compare various approaches for automatic selection of the GE members and propose several optimal methods, including a random selection, which consistently lead to a better performance of the driven RCPE. The comparison includes verification of near surface variables and precipitation using various verification metrics. The results are validated using several methods of model physics perturbation. Besides the selection of the optimal ensemble configurations, we show that at high precipitation intensities spatial up‐scaling is recommended in order to obtain useful probabilistic forecasts.
The impact of climate on topography, which is a theme in landscape evolution studies, has been demonstrated, mostly, at mountain range scales and across climate zones. However, in drylands, spatiotemporal discontinuities of rainfall and the crucial role of extreme rainstorms raise questions and challenges in identifying climate properties that govern surface processes. Here, we combine methods to examine hyperarid escarpment sensitivity to storm‐scale forcing. Using a high‐resolution DEM and field measurements, we analyzed the topography of a 40‐km‐long escarpment in the Negev desert (Israel). We also used rainfall intensity data from a convection‐permitting numerical weather model for storm‐scale statistical analysis. We conducted hydrological simulations of synthetic rainstorms, revealing the frequency of sediment mobilization along the sub‐cliff slopes. Results show that cliff gradients along the hyperarid escarpment increase systematically from the wetter (90 mm yr⁻¹) southwestern to the drier (45 mm yr⁻¹) northeastern sides. Also, sub‐cliff slopes at the southwestern study site are longer and associated with milder gradients and coarser sediments. Storm‐scale statistical analysis reveals a trend of increasing extreme (>10 years return‐period) intensities toward the northeast site, opposite to the trend in mean annual rainfall. Hydrological simulations based on these statistics indicate a higher frequency of sediment mobilization in the northeast, which can explain the pronounced topographic differences between the sites. The variations in landscape and rainstorm properties across a relatively short distance highlight the sensitivity of arid landforms to extreme events.
i) Further evaluation of the selected datasets of climate variables used as
input for hydrologic modelling led by thorough validation and bias correction
of modelled atmospheric parameters (only precipitation and
temperature) compared against in situ observations via statistical
analysis.
ii) The setup, validation, calibration, and parametric fine-tuning of the
hydrologic and maritime hydrodynamic models MODSUR and MeCSS,
respectively. Model evaluations were based on comparisons of simulation
outputs against in situ observations of hydrographic features (e.g. runoff
and coastal sea levels).
iii) The integrated coastal water resources modelling under climate change
the uncertainty that comprises separate hydrological and maritime
hydrodynamic modelling, a combination of model results, and production of plausible estimations for rainfall-run-off, river flow rates and
discharges, coastal barotropic currents and SSH fields, under the
influence of CC effects.
Using the ERA‐20C reanalysis and CRU TS4.03 observation based data, the study indicates a role of the rise in October–March mean seasonal surface pressure over the Near East (NE) in an intensification of moist air mass transport from Africa into the Eastern Mediterranean (EM) region during the last several decades. This yet non‐addressed relevant mechanism allows an explanation for the actual less intense than over the rest of the Mediterranean Region (MR) precipitation decline as well as the rise in frequency of extreme precipitation events in the southern part of the EM under the global warming conditions in recent decades. This factor appears to be contributing in slowing the global warming associated precipitation decline in the southeastern EM and significant changes in the structure of the regional precipitation leading to an increase in the contribution of extreme precipitation associated with an intensification of the moist air mass transport over northeastern Africa—Arabian Peninsula area.
Orographic impact on extreme sub‐daily precipitation is critical for risk management but remains insufficiently understood due to complicated atmosphere‐orography interactions and large uncertainties. We investigate the problem adopting a framework able to reduce uncertainties and isolate the systematic interaction of Mediterranean cyclones with a regular orographic barrier. The average decrease with elevation reported for hourly extremes is found enhanced at sub‐hourly durations. Tail heaviness of 10‐minute intensities is negligibly affected by orography, suggesting self‐similarity of the distributions at the convective scale. Orography decreases the tail heaviness at longer durations, with a maximum impact around hourly scales. These observations are explained by an orographically‐induced redistribution of precipitation towards stratiform‐like processes, and by the succession of convective cores in multi‐hour extremes. Our results imply a breaking of scale‐invariance at sub‐hourly durations, with important implications for natural hazards management in mountainous areas.
The Mediterranean has been recognized as a ‘hot spot’, currently influenced by climate change, and predicted to be strongly affected in the future by significant warming and drying. This trend is expected to be expressed in changes in the occurrence and intensity of Mediterranean cyclones, in general, and of East Mediterranean, i.e., Cyprus Lows, in particular, as well as in the occurrence of all other synoptic systems dominating the region.
In this dissertation, the semi-objective synoptic classification (Alpert et al., 2004a) was modified to investigate future changes in the occurrence of Eastern Mediterranean synoptic systems. The new classification was applied to eight CMIP5 models for the present (1986-2005), mid-21st century (2046-2065) and end of the century (2081-2100) periods, for both RCP4.5 and RCP8.5 scenarios. The new classification captured the synoptic systems' frequencies for the present period well, and particularly excelled in capturing that of the Cyprus Lows. A ~35% reduction in Cyprus Low occurrence is found towards the end of the 21st century (RCP8.5; Hochman et al., 2018a).
Following Hochman et al. (2018a), the seasons' definition of Alpert et al. (2004b) was applied to an ensemble of CMIP5 models to predict the changes in the lengths of Eastern Mediterranean seasons during the 21st century. It is shown that the ensemble adequately represents the annual cycle of the main synoptic systems over the Eastern Mediterranean. The analysis further suggests that at the end of the 21st century, the duration of the summer, characterized by the occurrence of the Persian Trough, is expected to be lengthened by 49%, while the winter, characterized by the occurrence of the Cyprus Low, is expected to be shortened by 56% under the RCP8.5 scenario (Hochman et al., 2018b). It is further shown that newly developed dynamical systems metrics of local dimension and persistence, based on daily sea level pressure, can serve as an extremely informative qualitative method for evaluating the predictability of a synoptic system, thus, potentially improving operational weather forecasts and enabling the evaluation of climate models' dynamics (Hochman et al., 2019).
Changes in the synoptic systems' occurrence and in the seasonal timing may influence precipitation and temperature regimes and result in severe environmental impacts. Therefore, the ability of 23 CMIP5 models, to represent extreme precipitation indices was evaluated for the Eastern Mediterranean and the Fertile Crescent regions. The models ensemble was then used to predict the extreme precipitation indices evolution in the 21st century under RCP4.5 and RCP8.5 scenarios. Over the Eastern Mediterranean, CMIP5 models agree on a future decrease in the following three extreme precipitation indices; total precipitation, consecutive wet days, and the number of wet days, by the values of 20-35%, 10-20%, and 20-35%, respectively. In the Fertile Crescent, extremely wet days (P95) are expected to increase by ~25%, except for the south eastern coasts of the Mediterranean Sea, which show significant decreases in P95, particularly for RCP8.5 and at the end of the 21st century (Samuels et al., 2017).
Finally, High resolution climate projections over Israel (about 8 km) have been obtained with the regional model COSMO-CLM, nested into the CORDEX-MENA CMCC-CM simulations at 25 km resolution. This simulation provides high-resolution spatial variability of total precipitation and precipitation intensity. Projections are presented not only in terms of average properties but also using a subset of extreme temperature and precipitation indices, taken from the standard Expert Team on Climate Change Detection and Indices, for the period 2041-2070 with respect to 1981-2010 (RCP4.5).
A general increase in seasonal mean temperature is projected throughout the domain with peaks of ~2.5°C, especially in winter and autumn. Extreme temperature indices show increases, larger in the minimum than in the maximum temperatures. Regarding total seasonal precipitation, decreases were found in the north and central parts of Israel, characterized by Mediterranean climate, with reductions reaching ~40%, and increases of the same percentage in the most southern parts of Israel, i.e., the hyper-arid region, during winter and spring. An increase in precipitation intensity is shown mostly for the southern, hyper-arid, part of the region, with some indications of extremity also in the northern, Mediterranean climate, part of the country (Hochman et al., 2018c, d).
Predicted changes in the occurrence of the various synoptic systems in general and of Cyprus Lows, in particular, will lead to a more accurate prediction of local potential climatic hazards. Furthermore, the projected changes in the seasons' length may lead to substantial changes in the hydrological regime and water resources, reduce the potential of dry farming, increase the risk of fires and air pollution and change the timing of seasonal health hazards. The outcomes of the articles published within the frame of this dissertation may serve as a basis for priority setting and policy formulation towards climate adaptation at the regional level and motivate enhanced GHG mitigation.
The Red Sea trough (RST) is a low‐pressure trough extending from south towards the Levant. Unlike previous synoptic classifications covering all systems that affect the region, our algorithm focuses on the RST alone. It uses sea‐level pressure (SLP) and relative geostrophic vorticity for identifying the existence of an RST and classifying it to one of three types, according to the location of the trough axis with respect to 35°E longitude. The following conditions were imposed to assure the existence of an RST: (a) north to south SLP drop across the Levant, (b) average positive sea‐level relative vorticity over the region of interest, (c) existence of a distinct and continuous trough axis from the south towards the region of interest and (d) absence of any pronounced closed cyclone near the Levant. The algorithm was applied on the NCEP/NCAR reanalysis, 2.5° × 2.5° resolution and the ERA‐Interim, 2.5° × 2.5° and 0.75° × 0.75° resolutions. An evaluation of the algorithm against subjective identification, based on the NCEP reanalysis, showed an agreement of 93% for RST identification and 79% for correct classification. The use of fine resolution data may insert noise that reduce the identification rate of RSTs but improves the axis locating. The autumn is the main season of RST, with a maximum in November and a consistent decrease towards the July minimum. The annual frequency varies among the data sources between 17.6 and 24.6%. The trough axis is shown to have a diurnal oscillation; towards the eastern coast of the Mediterranean at nighttime and eastward, inland, at noontime. No consistent long‐term trend was found for the period 1979–2016, during which the global warming was persistent. This automated algorithm is flexible in the sense that it is not confined to any predetermined spatial resolution and is applicable to operational forecast model as well as to climate model outputs.
The Mediterranean region is projected to be significantly affected by climate change through warming and drying. The Eastern Mediterranean (EM) is particularly vulnerable since the bulk of the precipitation in the region is associated with a specific circulation pattern, known as Cyprus Low (CL). Here, we study the influence of increased greenhouse gases on the average properties and dynamics of CLs, using a regional semi-objective synoptic classification. The classification is applied to NCEP/NCAR reanalysis data for the present day (1986–2005) as well as to eight CMIP5 models for the present day and for the end of the century (2081–2100; RCP8.5). This is complemented by a dynamical systems analysis, which is used to investigate changes in the dynamics and intrinsic predictability of the CLs. Finally, a statistical downscaling algorithm, based on past analogues, is applied to eighteen rain stations over Israel, and is used to project precipitation changes associated with CLs. Significant changes in CL properties are found under climate change. The models project an increase in CL meridional pressure gradient (0.5–1.5 hPa/1000 km), which results primarily from a strong increase in the pressure over the southern part of the study region. Our results further point to a decrease in CL frequency (− 35%, as already noted in an earlier study) and persistence (− 8%). Furthermore, the daily precipitation associated with CL occurrences over Israel for 2081–2100 is projected to significantly reduce (− 26%). The projected drying over the EM can be partitioned between a decrease in CL frequency (~ 137 mm year⁻¹) and a reduction in CL-driven daily precipitation (~ 67 mm year⁻¹). The models further indicate that CLs will be less predictable in the future.
Previous studies revealed that the interannual variation of precipitation in the northwest of Iran (NWI) was controlled mainly by the Mediterranean cyclones and local mechanisms. Drawing upon the literature, the aim of this study is twofold: examining precipitation variability resulting from each of the abovementioned mechanism and investigating variation in precipitation regime in the NWI during 1961–2010. To provide a better understanding of the features of precipitation regime in the NWI, in the present study, I put the spotlight on the changes in precipitation patterns occurring over five decades in a context experiencing climate change. Accordingly, the annual, semiannual, and triple cycle of precipitation data from 1961 to 2010, which were obtained from 250 stations and by which a gridded dataset of monthly precipitation for the period above was created, were analyzed using harmonic analysis. The results showed that the regional average of precipitation during five successive decades decreased from 385.8 mm in the first decade to 297.3 mm in the last decade. The differences in the precipitation values during the five decades under study can be due to the slight positive trends in precipitation in summer and considerable negative trends in other seasons. Moreover, global warming and changes in the path of storm tracks can be considered as the possible reasons behind the observed changes in the precipitation in the NWI.
Large positive and negative sea level anomalies on the coast of the Mediterranean Sea are linked to intensity and position of cyclones moving along the Mediterranean storm track with dynamics involving different factors. This analysis is based on a model hindcast and considers nine coastal stations, which are representative of sea level anomalies with different magnitudes and characteristics. When a shallow water fetch is present, the wind around the cyclone centre is the main cause of positive and negative sea level anomalies, depending on its onshore or offshore direction. The inverse barometer effect produces a positive anomaly on the coast near the cyclone pressure minimum and a negative anomaly at the opposite side of the Mediterranean Sea. The latter is caused by the cross-basin mean sea level pressure gradient that is associated with the presence of a cyclone. This often coincides with the presence of an anticyclone above the station, which causes a local negative inverse barometer effect. Further, at some stations, negative sea level anomalies are reinforced by a residual water mass redistribution within the basin, which is associated with a transient response to the atmospheric pressure forcing. Though the link with the presence of a cyclone in the Mediterranean has comparable importance for positive and negative anomalies, the relation between cyclone position and intensity is stronger for the magnitude of positive events. The area of cyclogenesis, track of the central minimum and position at the time of the event differ depending on the location the sea level anomaly occurs and on its sign. The western Mediterranean is the main cyclogenesis area for both positive and negative anomalies overall. Atlantic cyclones mainly produce positive sea level anomalies in the western basin. At the easternmost stations, positive anomalies are caused by cyclogenesis in the eastern Mediterranean. North African cyclogenesis is a major source of positive anomalies on the central African coast and negative anomalies on the eastern Mediterranean and northern Aegean coasts.
Environmental risks posed by oil spills in semi-enclosed basins are more pronounced than those in the open ocean due to potential deposition along long segments of the coastlines. As a semi-enclosed sea, the Mediterranean is highly vulnerable to pollution events. Recent discoveries of major oil and natural gas reserves in the eastern Levantine basin have led to accelerated drilling, with several countries at various stages of exploration and production and others having mapped blocks for licensing, thereby significantly increasing the risks of a potential spill. Due to drilling by multiple, adjacent countries, any spills from deep water wells will be prone to cross border transport due to the highly variable winds and ocean currents. This risk is assessed through a series of simulations with an oil spill model forced with high resolution ocean currents and winds. The scenarios considered are well blowouts of several weeks duration, located within the drilling zones of each of various countries. Models such as this provide the basis for further environmental assessment and risk analysis. They also emphasize the importance of multinational cooperation to respond to and mitigate the environmental impacts which would result from a potential oil spill from any of the countries involved.
Prezentowana tu praca stanowi wynik realizacji projektu badawczego p.t.
„Współczesne zmiany aktywności niżów śródziemnomorskich jako czynnik ryzyka
ekstremalnych zdarzeń hydrometeorologicznych i zmian klimatycznych
w Polsce”. Zebrano w niej wyniki klimatologicznych badań niżów śródziemnomorskich,
oddziałujących na warunki klimatyczne w Polsce w latach 1958-2008.
Projekt realizowano w Katedrze Geografii Fizycznej Uniwersytetu Łódzkiego.
Opracowanie składa się z wprowadzenia, przedstawiającego specyfikę
badanych cyklonów – niżów śródziemnomorskich i odwołującego się m.in. do
klasycznego ujęcia tych niżów, wędrujących szlakiem „Vb” nad Europą i zobrazowanego
mapą torów niżowych van Bebbera z 1891 roku. Drugi rozdział
poświęcono prezentacji celów i zakresu opracowania; przedstawiono problemy
i hipotezy badawcze. W kolejnym rozdziale opisano wykorzystane dane
i materiały oraz zastosowane metody ich analizy.
W rozdziale 4. zawarto wyniki oceny częstości występowania niżów śródziemnomorskich,
jej zmienność sezonową oraz wyróżniono typy szlaków wędrówki
niżów nad Europą Środkowo-Wschodnią. Rozdział 5. zawiera ocenę
wysokości opadów o genezie śródziemnomorskiej oraz ich udział w całkowitych sumach opadów w Polsce. W rozdziale 6. przedstawiono m.in. obraz rozmieszczenia
opadów pochodzenia śródziemnomorskiego w Polsce i ich związek
z torami ruchu niżów. Rozdział 7. zawiera ocenę zawartości wilgoci („precipitable
water”) w warunkach działalności niżów śródziemnomorskich na obszarze
Polski oraz ocenę wpływu tej zawartości na wysokość opadów. Pokazano
także strukturę pól temperatury i wilgotności w Europie związanych z niżami
śródziemnomorskimi. Kolejny, 8. rozdział prezentuje wyniki badania wieloletnich
zmian częstości i aktywności niżów śródziemnomorskich, zmian opadów
pochodzenia śródziemnomorskiego w Polsce i zmian zawartości wilgoci
w atmosferze. Przedstawiono także m.in. próbę wyjaśnienia tych zmian,
wskazując na równoległą ewolucję makroform cyrkulacji atmosferycznej.
W rozdziale 9 przedstawiono wyniki analizy cyrkulacji atmosferycznej w górnej
troposferze (na poziomie 300 hPa), która najwyraźniej kształtuje aktywność
badanych niżów i potwierdza dywergencyjną teorię cyklogenezy.
W podsumowaniu (rozdz. 10) zebrano najważniejsze wyniki, w tym m.in.
wniosek, że wykonane analizy statystyczne nie potwierdziły popularnej hipotezy
o rosnącej częstości zdarzeń ekstremalnych (tu: częstości i aktywności
niżów Vb) w epoce postępującego ocieplenia klimatu.
ResearchGate has not been able to resolve any references for this publication.