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Topographic map of the Meteor Crater (a) and the locations of the instrumented towers inside the crater (b). Contour interval is 20 m in (a) and 10 m in (b)
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Observations from a recent meteorological experiment in the Meteor Crater, a small, near circular, enclosed basin, in northern
Arizona of the United States, are used to investigate the status of the atmosphere in the basin as indicated by temperature
inversion and its relationship to ambient atmospheric conditions. Strong synoptic winds aloft do no...
Contexts in source publication
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... 165 m deep and 1200 m in diameter at the rim level. The rim of the crater, which has no major paths, rises approximately 50 m above the surrounding plain on the Colorado Plateau. The crater floors and sidewalls are primarily rocks that are sparsely covered with grasses and small bushes. The topography of the Meteor Crater is shown in Fig. 1 along with measurement sites used in this ...
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... fluxes, and radiative and soil fluxes were made inside the crater with an array of micrometeorological flux towers or ISFF (Integrated Surface Flux Facility) supplied, installed, and operated by the National Center for Atmospheric Research (NCAR)'s Earth Observing Laboratory (EOL). The towers were located on an east-west cross section ( Fig. 1) with a 9 m tower near the center of the crater (FLR) and on the lower east and west sidewalls (EL and WL), and a 6 m tower on the upper slope of the east and west sidewalls (EU and WU). In addition to the five flux towers inside the crater, a 10 m tripod was used to collect data at the highest point (1744 m above ground level or AGL) ...
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... meteorological conditions were monitored by a mini-sodar and a Radio Acoustic Sounding System (RASS) at a location about 2.5 km southwest of the crater (SW in Fig. 1). The mini-sodar and RASS provide wind and temperature profiles from about 10 m to 200-300 m above the surface at 10 m height interval. An ISFF was co-located at the mini-sodar=RASS site to provide surface observations of mean and turbulence variables. This site was chosen based on a climatological analysis of surface meteorological ...
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... prevailing surface wind direction for the month of October is southwest. Upper-air meteorological conditions were also observed by NCAR EOL's Integrated Sounding System (ISS) consisting of a 915-MHz radar wind profiler with RASS and a 10 m enhanced weather tower. The ISS site was located approximately 5 km north-northwest of the crater (ISS in Fig. 1) to avoid radio interference with the RASS at the SW mini-sodar site. During the seven IOPs, Vaisala RS92 GPS radiosondes were launched from the ISS sites every three hours, starting at 1500 MST and ending at 0900-1100 MST the next morning, to document the large-scale background atmospheric conditions. Detailed descriptions of the ...
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... properties are expected to be also quite different. Figures 10 and 11 show average nighttime turbulent kinetic energy (TKE), friction velocity (u à ), and sensible heat flux (w 0 t 0 ) at the 0.5 m level on the floor tower (FLR) for each night of the month. For the fully decoupled nights, Richardson number exceeded the critical Richardson number most of the time (Fig. 8c) Fig. 9. ...
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... the net longwave radiation loss at night does not appear to be a good indicator for whether the basin atmosphere would be decoupled from the ambient environment, the strength of the temperature inversion appears to be positively correlated to the loss of longwave radiation. Figure 13 shows scatter plots of the nighttime integrated inversion strength as a function of nighttime integrated longwave radiation loss measured at each of the five towers inside the crater. There is a clear correlation about the inversion strength and the radiation loss measured at the two upper sidewall towers, with the 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 (1) inversion increasing exponentially with the increase of radiation loss. ...
Similar publications
The interactions between a katabatic flow on a plain and a circular basin cut into the plain and surrounded by an elevated rim were examined during a 5-h steady-state period during the Second Meteor Crater Experiment (METCRAX II) to explain observed disturbances to the nocturnal basin atmosphere. The approaching katabatic flow split horizontally ar...
Observations are analyzed to explain an unusual feature of the nighttime atmospheric structure inside Arizona's idealized, basin-shaped Meteor Crater. The upper 75%-80% of the crater's atmosphere, which overlies an intense surface-based inversion on the crater's floor, maintains a near-isothermal lapse rate during the entire night, even while conti...
Citations
... Pseudo vertical temperature gradients have been evaluated from ground-based meteorological networks, either from permanent observatories (Pepin, 2001;Rolland, 2003;Kirchner et al., 2013;Largeron and Staquet, 2016a;Navarro-Serrano et al., 2018;Joly and Richard, 2019;Kikaj et al., 2019) or temporary networks installed ad hoc during experimental campaigns (Whiteman et al., 2004;Steinacker et al., 2007;Mir o et al., 2018). Variability of the vertical structure of the atmosphere during CAPs has been also studied using radiosondes, tethered balloons, SODAR, or airplanes (Wolyn and Mckee, 1989;Clements et al., 2003;Yao and Zhong, 2009;Lareau et al., 2013;Lehner et al., 2015;McCaffrey et al., 2019). The dynamics of those events have been simulated through mesoscale models (Largeron and Staquet, 2016b;Lehner et al., 2017;Pagès et al., 2017;Flores et al., 2020). ...
Cold air pools (CAPs) are one of the most severe weather conditions experienced across many basins worldwide, related to episodes of extreme cold temperatures, poor air quality, and disruption of transportation networks. This study offers a basic climatology of CAPs in the southern Spanish Plateau and investigates its evolution since 1961 and their links with local, synoptic, and large‐scale climate variability. It is based on the comparison of meteorological records from two stations, one in the Sistema Central Range (Navacerrada, 1,894 m asl) and another at the plain (Madrid‐Barajas, 609 m asl). Accuracy and representativeness of both locations to depict the spatial and temporal variability of CAPs was also tested. CAPs days (defined as the simultaneous occurrence of a daily minimum temperature difference above 0.1°C between both stations) were found to occur year‐round, but the most frequent and intense occur in winter (NDJ). Some typical features of CAPs, such as local mesoscale processes (katabatic and anabatic flows) in connection with synoptic (advection of mid‐troposphere warm air masses during high‐pressure regimes) and hemispheric (a positive phase of the North Atlantic Oscillation) variability were also observed, leading to a sheltered boundary layer at the bottom of southern Spanish Plateau, decoupled from the free troposphere. By night, CAPs have maintained both their frequency and intensity, which means that the frequency of extremely cold nights on the plain has remained relatively stable (despite global warming). By day, an enhanced warming of the high‐elevation site has increased the temperature difference between the mountains and the plain during CAP days.
... In the GZM, the strongest and longest SBI occurred in autumn when wind speeds and cloudiness factors were lower than those in winter [93]. The frequency of all day-round SBI is low, unlike that observed at higher latitudes [8,23,24,27,32,94,95] and in concave terrains [9,26,70,96,97], due to shorter nights and milder weather conditions and more exposure to general weather conditions in upland conditions than in valleys and basins. Daytime SBI mainly occurs in summer, when favorable weather conditions for SBI development are more frequent than in winter. ...
This paper studies surface air temperature inversions and their impact on air pollution under the background of meteorological conditions in southern Poland. The relationship of temperature gradients and air quality classes with weather conditions in the most urbanized and polluted part of Poland as represented by the Upper Silesia region (USR) within the administrative boundaries of the Górnośląsko-Zagłębiowska Metropolis (GZM) is presented. Based on probability analysis this study hierarchized the role of the selected weather elements in the development of surface-based temperature inversion (SBI) and air quality (AQ). The thresholds of weather elements for a rapid increase in the probability of oppressive air pollution episodes were distinguished. Although most SBI occurred in summer winter SBIs were of great importance. In that season a bad air quality occurred during >70% of strong inversions and >50% of moderate inversions. Air temperature more strongly triggered AQ than SBI development. Wind speed was critical for SBI and significant for AQ development. A low cloudiness favored SBI occurrence altered air quality in winter and spring during SBI and favored very bad AQ5 (>180 µg/m3) occurrence. The probability of high air pollution enhanced by SBI rapidly increased in winter when the air temperature dropped below −6 °C the wind speed decreased below 1.5 m/s and the sky was cloudless. Changes in the relative humidity did not induce rapid changes in the occurrence of bad AQ events during SBI
... Unfortunately, there have been relatively few observational studies of PTI events (Clements et al., 2003;Dorninger et al., 2011;Lareau et al., 2013;Lehner et al., 2015;Silcox et al., 2012). To date, this lack of observational studies has mainly been due to the difficulty in making the necessary meteorological measurements within the topographically challenging regions (Yao and Zhong, 2009). Furthermore, such studies often require the deployment of sophisticated instrumentation (e.g., radiosondes, tethered balloons, masts, or aircraft), which is typically expensive and labor intensive to operate (Baasandorj et al., 2017). ...
One year of meteorological and atmospheric radon observations in a topographically complex subalpine basin are used to identify persistent temperature inversion (PTI) events. PTI events play a key role in public health due to the accumulation of urban pollutants that they cause. Two techniques are compared: a new radon-based method (RBM), based on single-height ²²²Rn measurements from a single centrally located station, and an existing pseudo-vertical temperature gradient method (TGM) based on observations from eight weather stations around the subalpine basin. The RBM identified six PTI events (four in winter, two in autumn), a subset of the 17 events identified by the TGM. The RBM was more consistent in its identification of PTI events for all seasons and more selective of persistent strongly stable conditions. The comparatively poor performance of the TGM was attributed to seasonal inconsistencies in the validity of the method's key assumptions (influenced by mesoscale processes, such as local drainage flows, nocturnal jets, and intermittent turbulence influence) and a lack of snow cover in the basin for the 2016–2017 winter period. Corresponding meteorological quantities for RBM PTI events (constituting 27 % of the autumn–winter cold season) were well characterized. PTI wind speeds in the basin were consistently low over the whole diurnal cycle (typically 0.2–0.6 m s⁻¹). Suitability of the two techniques for air quality assessment was compared using hourly PM10 observations. Peak PM10 concentrations for winter (autumn) PTI events were underestimated by 13 µg m⁻³ (11 µg m⁻³) by the TGM compared with the RBM. Only the RBM indicated that nocturnal hourly mean PM10 values in winter PTI events can exceed 100 µg m⁻³, the upper threshold of low-level short-term PM10 exposure according to World Health Organization guidelines. The efficacy, simplicity, and cost effectiveness of the RBM for identifying PTI events has the potential to make it a powerful tool for urban air quality management in complex terrain regions, for which it adds an additional dimension to contemporary atmospheric stability classification tools. Furthermore, the long-term consistency of the radon source function will enable the RBM to be used in the same way in future studies, enabling the relative magnitude of PTI events to be gauged, which is expected to assist with the assessment of public health risks.
... Unfortunately, there have been relatively few observational studies of PTI events ( Clements et al., 2003;Dorninger et al., 2011;Lareau et al., 2013;Lehner et al., 2015;Silcox et al., 2012). To date, this lack of observational studies has mainly been due to the difficulty in making the necessary meteorological measurements within the topographically-challenging regions (Yao and Zhong, 2009). Furthermore, such 35 studies often require the deployment of sophisticated instrumentation (e.g., radiosondes, tethered balloons, masts or aircraft), which are typically expensive and labour intensive to operate. ...
One year of meteorological and atmospheric radon observations in a topographically-complex Subalpine Basin are used to identify ‘persistent temperature inversion’ (PTI) events. PTI events play a key role in public health due to the accumulation of urban pollutants that they cause. Two identification techniques are compared: a new method, based on single-height radon measurements from a single centrally-located station, and an existing approach based on observations from eight weather stations around the Subalpine Basin. After describing the radon-based method (RBM), its efficacy is compared with that of the existing pseudo-vertical temperature gradient method (TGM). The RBM identified 6 PTI events over the year (4 in winter, 2 in autumn), a subset of the 17 events identified by the TGM. The RBM is demonstrated to be more consistent in its identification of PTI events, and more selective of persistent strongly stable conditions. Furthermore, its performance is seasonally independent. The comparatively poor performance of the TGM was attributed to seasonal inconsistencies in the validity of the method’s key assumptions (influenced by mesoscale processes, such as local drainage flows, nocturnal jets, and intermittent turbulence influence), and a lack of snow cover in the basin for the 2016–2017 winter period. Corresponding meteorological quantities for RBM PTI events (constituting 27 % of the autumn–winter cold season), were well characterised. PTI wind speeds in the basin were consistently low over the whole diurnal cycle (typically 0.2–0.6 m s−1). The comparative efficacy of the RBM for PTI air quality assessment is demonstrated using hourly PM10 observations throughout the year. Peak hourly mean PM10 concentrations for winter (autumn) PTI events were underestimated by 13 µg m−3 (11 µg m−3) by the TGM compared with the RBM. Only the RBM indicated that nocturnal hourly mean PM10 values in winter PTI events can exceed 100 µg m−3, the upper threshold of low-level short-term PM10 exposure according to World Health Organisation guidelines. The efficacy, simplicity and cost effectiveness of the RBM for identifying PTI events has the potential to make it a powerful tool for urban air quality management in complex terrain regions; for which it adds an additional dimension to contemporary atmospheric stability classification tools. Furthermore, the long-term consistency of the radon source function will enable the RBM to be used in the same way in future studies, enabling the relative magnitude of PTI events to be gauged, which is expected to assist with the assessment of public health risks.
... Una de las principales características del fenómeno de inversión térmica es la estabilidad estática que restringe el intercambio turbulento y el arrastre entre la baja atmósfera y la atmósfera libre (Bourne, 2008), limitando el transporte de contaminantes emitidos desde la superficie (limita la ventilación), con implicaciones en las condiciones de la calidad del aire (Rendón et al., 2015(Rendón et al., , 2014Wallace et al., 2010;Yao y Zhong, 2009;Janhäll et al., 2006;Anquetin et al., 1998). Además, en valles urbanizados, las tasas de emisión suelen ser altas, debido al desarrollo de múltiples actividades industriales y de transporte (Wallace et al., 2010), lo que causa que el efecto combinado de las altas tasas de emisión y de la limitada ventilación, pueda dar lugar a serios problemas de contaminación del aire, y con esto, ocasionar problemas de salud pública (Sabzevari et al., 2014;Bourne, 2008). ...
As a result of the combination of limited ventilation and high emission of pollutants, urban valleys may experience serious air pollution problems. Ventilation can be limited not only by orographic barriers, but also by the capping effect associated with a low level temperature inversion. Temperature inversion can strongly affect the air quality of an urban valley due to its influence on the air exchange between the upper atmosphere and the bottom of the valley. In this sense, the Aburrá Valley (Colombia) posses a complex and highly urbanized topography, where the occurrence of temperature inversions has been reported regularly. Through the analysis of real temperature data from the local atmosphere during 2015 and 2016, we characterize the formation and breaking processes of the atmospheric high stability layers, as well as their seasonal variability. Finally, we discuss the implications of these events on the valley's air quality.
Los valles urbanizados pueden experimentar serios problemas de contaminacion
atmosferica, como resultado del efecto combinado de su limitada ventilacion y de la alta emision de contaminantes desde las areas urbanas. La ventilacion puede ser limitada no solo por las barreras orograficas, sino tambien por el efecto de estancamiento asociado con la ocurrencia de capas estables o de inversion termica cerca de la superficie. La ocurrencia de estas capas de inversion termica puede afectar fuertemente la calidad del aire de un valle urbano debido a su infuencia en el intercambio de aire entre las capas mas superficiales y la atmosfera superior. Una mejor comprension de las caractersticas de las inversiones termicas y su relacion con la calidad del aire es de particular importancia para los procesos de toma de decisiones, en particular aquellos relacionados con la planeacion urbana en
ciudades en desarrollo, ubicadas en terrenos de montaña. De manera particular, el Valle de Aburra (Colombia) es un valle de topografia compleja y altamente urbanizado, en donde se ha reportado la ocurrencia de inversiones termicas con regularidad. A traves de un analisis de informacion observada de la temperatura real de la atmosfera local durante los años 2015 y 2016, se caracteriza el proceso de formacion y de rompimiento de las capas de alta estabilidad atmosferica, asi como su variabilidad estacional. Finalmente, se discuten las implicaciones de estos eventos en la calidad del aire del valle.
... Numerous other complications are not addressed in the above classification of cold pools, including the structure of the upwind larger-scale flow (Yao and Zhong 2009). Up-valley regional flow may intensify the up-valley cold pool by blocking the down-valley outflow of cold air (LeMone et al. 2003). ...
Stratified nocturnal flow above and within a small valley of approximately 12-m depth and a few hundred metres width is examined as a case study, based on a network of 20 sonic anemometers and a central 20-m tower with eight levels of sonic anemometers. Several regimes of stratified flow over gentle topography are conceptually defined for organizing the data analysis and comparing with the existing literature. In our case study, a marginal cold pool forms within the shallow valley in the early evening but yields to larger ambient wind speeds after a few hours, corresponding to stratified terrain-following flow where the flow outside the valley descends to the valley floor. The terrain-following flow lasts about 10 h and then undergoes transition to an intermittent marginal cold pool towards the end of the night when the larger-scale flow collapses. During this 10-h period, the stratified terrain-following flow is characterized by a three-layer structure, consisting of a thin surface boundary layer of a few metres depth on the valley floor, a deeper boundary layer corresponding to the larger-scale flow, and an intermediate transition layer with significant wind-directional shear and possible advection of lee turbulence that is generated even for the gentle topography of our study. The flow in the valley is often modulated by oscillations with a typical period of 10 min. Cold events with smaller turbulent intensity and duration of tens of minutes move through the observational domain throughout the terrain-following period. One of these events is examined in detail.
... Upstream terrain blocking and nocturnal drainage flows have also been identified as factors that can contribute to the formation of persistent VCPs (Zängl, 2003;Katurji and Zhong, 2012). Turbulent erosion induced by strong wind shear near the top of VCPs has been suggested as a plausible mechanism for the elimination of persistent temperature inversions (Vergeiner, 1996;Zhong et al., 2003;Yao and Zhong, 2009;Lareau and Horel, 2015a), although the rate of erosion by turbulence is too slow to completely remove the inversion without the help from other processes. The presence of low-level clouds and fog has been found to influence inversion strengths during the maintenance phase of persistent VCPs by altering surface energy balance (Wolyn and McKee, 1989;Zhong et al., 2001;Neemann et al., 2015). ...
Valleys can trap cold air to form Valley Cold Pools (VCPs). Characterized by stable stratification and weak winds, VCPs, especially those that last over multiple days, can produce adverse effects such as poor visibility and severe air pollution. Using the gridded data set of the North American Regional Reanalysis (NARR) for the period of 1979 through 2012, this study examines the climatology of VCPs in the western United States with a focus on spatial and temporal variability. The results reveal a widespread occurrence of short-lived (1–2 days) VCPs over both the mountainous areas of the West and the Northern Plains. Longer VCP episodes, however, tend to be limited to large basins/valleys in the Northwest and the Intermountain West. The leading mode of variability in the annual number of cold-season multi-day VCP event anomalies appears to be linked to a sea-surface temperature anomaly pattern typically found during the warm phase of Pacific Decadal Oscillation. Corresponding to the positive phase of the leading mode of variability is an anomalous 500-hPa ridge over the western United States induced by a Rossby wave train, which, by blocking cold-air intrusions and producing mid-level subsidence warming, leads to more persistent VCP episodes in the western United States. In addition to large-scale wintertime circulation anomalies, local surface temperature anomalies also contribute to the variability.
... Urban valleys can experience serious air pollution problems as a combined result of their limited ventilation and the high emission of pollutants from the urban areas (e.g., Rutllant and Garreaud 1995;Malek et al. 2006;Chu et al. 2008). In such complex terrains, the venting of pollution out of the valley is limited by the topography and can be further restricted by local circulations (Gohm et al. 2009), and particularly by urban heat island-induced circulations (Haeger-Eugensson and Holmer 1999;Savijärvi and Liya 2001) and low-level temperature inversions (Janhall et al. 2006;Yao and Zhong 2009;Rendón et al. 2014). The occurrence of inversion layers near the ground, that is layers where the potential temperature increases with height (Whiteman 1982), are common in urban areas and mountain valleys (Oke 1995;Whiteman 2000). ...
Urban valleys can experience serious air pollution problems as a combined result of their limited ventilation and the high emission of pollutants from the urban areas. Idealized simulations were analysed in order to elucidate the breakup of an inversion layer in urban valleys subject to a strong low-level temperature inversion and topographic effects on surface heating such as the topographic shading, as well as the associated air pollution transport mechanisms. The results indicate that the presence and evolution in time of the inversion layer and its interplay with an urban heat island within the valley strongly influence the venting of pollutants out of urban valleys. Three mechanisms of air pollution transport were identified. These are transport by upslope winds, transport by an urban heat island-induced circulation, and transport within a closed slope-flow circulation below an inversion layer.
... En el caso de Cabezo de la Plata, al originarse normalmente un estrato muy cálido (15-19 ºC) a 200-300 m de altitud, la masa de aire más frío (N) no puede reemplazarlo, y se desliza en forma de cuña hacia lugares más bajos. No hay que olvidar, y éste es el caso, la influencia que en tales situaciones ejercen los flujos de aire frío catabático (Yao y Zhong, 2009). ...
[Es] En el Sureste peninsular son frecuentes las situaciones anticiclónicas alimentadas en invierno por la dorsal subtropical marítima. Bajo estas condiciones, las cuencas y valles fluviales intrabéticos son bastante proclives al desarrollo de inversiones térmicas. Un claro ejemplo lo constituye la Vega Media del Segura en los meses de invierno, especialmente cuando el enfriamiento nocturno del suelo aparece acompañado por movimientos de aire anticiclónico subsidente, advecciones cálidas de componente SO a niveles bajos atmosféricos y flujos fríos catabáticos procedentes de la Sierra de Carrascoy. En el presente artículo se analizan tales factores y las situaciones de inversión térmica más importantes registradas en esta Vega durante el período 2000-2011. Para ello se han utilizado los datos de las estaciones meteorológicas y de los sondeos aerológicos disponibles en el área, en particular los relativos a régimen de temperaturas, estratificación térmica vertical e indicadores de estabilidad atmosférica.
PALABRAS CLAVE: inversión térmica; anticiclón; advección cálida; Vega Media del Segura; Región de Murcia.
[En] Anticyclonic situations fed by the maritime subtropical dorsal in winter are frequent in the South-east Spain. Under these conditions, the intrabaetic depressions and fluvial valleys are prone to thermal inversions. A clear example is the Middle Valley of the Segura River during winter months, especially when cooling at night appears to be accompanied by anticyclonic subsident air, warm advection SW flows at low atmospheric levels and cold katabatic winds proceeding from Sierra de Carrascoy. Such factors and the most temperature inversion situations registered in the study area during the period 2000-2011 are analyzed in this work. For this purpose data of meteorological stations and aerological soundings (e.g. temperature regime, vertical thermal mstratification, indicators of atmospheric stability) were used.
KEY WORDS: temperature inversion; anticyclone; warm advection flow; Vega Media del Segura river; Murcia Region.
[Fr] Les situations anticycloniques alimentées pendant l’hiver par la dorsale maritime subtropicale sont fréquentes dans le Sud-est espagnol. Dans ces conditions, les bassins et vallées fluviales intrabétiques sont assez enclins au développement d’inversions thermiques. La Vega media del Segura (vallée moyenne du fleuve) constitue un clair exemple pendant les mois d’hiver, spécialement quand le refroidissement nocturne du sol apparaît accompagné par des mouvements d’air anticyclonique subsidente, advections chaudes de direction générale SO à de bas niveaux atmosphériques et flux froids catabatiques provenant de la Sierra de Carrascoy. L’objectif de cette recherche est d’analyser ces factors et les situations d’inversion thermique les plus importantes dans l’aire pendant la période 2000-2011. Pour cela, nous avons utilisé les données des stations météorologiques et des sondages aerologiques disponibles dans l’aire, en particulier, les relatifs au régime de températures, de stratification thermique verticale et d’indicateurs de stabilité atmosphérique.
MOTS CLÉS: inversion thermique; anticyclone; advection d’air chaud; Plaine Moyenne du Segure; région de Murcie.
... An important factor in controlling the severity and cessation of cold air drainage is the sky view (Whiteman et al., 2004). Thus, sheltered and pronounced local hollows, such as sinkholes or craters, encourage drainage (Clements et al., 2003; Whiteman et al., 2004; Yao and Zhong, 2009). Cooling ceases when the net radiative flux balances the sum of the ground, latent and sensible heat fluxes, although the last two are generally small in light wind situations. ...
Cold air drainage is a characteristic of hilly or mountainous terrain and can have significant impact on agricultural or horticultural activities. This paper considers a range of synoptic and topographic factors that could affect the phenomenon of cold air drainage, through an exploration of its characteristics in the Peak District of central England, showing that cold air drainage events can occur at any time of the year, with summer events being even more frequent than those usually noticed in winter. The occurrence of such events is related to the local topography, and particularly the correspondence to hollows and local valleys on the scale of 0.5-1 km, rather than on the scale of the principal drainage routes in the region. In contrast to some previous studies, synoptic and local weather conditions were not found to be strong indicators of cold air drainage events. It is also shown that under suitable conditions cold air drainage can overcome the effects of the urban heat island. © 2012 Royal Meteorological Society.
