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Sea ice cover (shaded) and EADY growth rate (isolines) for the homogeneous case at 16 UTC. Sea ice cover isolines from 60 % to 80 %, increment 5 %. EADY growth rate isolines from 0·10 −4 s −1 to 1·10 −4 1 −1 , increment 2·10 −5 1 −1 .
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Polar mesocyclones are small-scale, short-living phenomena in the Arctic and Antarctic. Their forecast is difficult due to a lack of knowledge of initial and boundary conditions. Idealised sensitivity studies are performed with the mesoscale atmosphere - sea ice model METRAS-MESIM to evaluate the relevance of the large-scale meteorological situatio...
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... this time areas of enhanced baroclinicity develop over the ice as a result of the ice drift caused by the mesocyclone. These regions occur where the sea ice concentration is reduced during the mesocyclone passage (Figure 7). Thus, the action of a mesocyclone on the sea ice can be the reason for enhanced baroclinicity, which finally can result in an intensification of a mesocyclone. ...
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Citations
... This converging flow constitutes a low-level baroclinic instability and enhances cyclonic vorticity due to vortex stretching, thereby increasing the PV anomaly . As a measure for baroclinicity we calculate the maximum Eady growth rate (σ max in s −1 ; Dierer & Schluenzen, 2005;Eady, 1949;Lindzen & Farrell, 1980) that describes how well deep pressure systems can develop in a weather situation over a specific area, with positive values favoring cyclogenesis: ...
... Within the next 6 hr, the katabatic flow from Ammassalik triggers a polar low with closed isobars on 29 February at 00 UTC and a core pressure of less than 980 hPa (Figure 2e). Converging flow, differential cold air advection decreasing with height in the Ammassalik area trigger the formation of the polar low near the sea ice edge, where polar lows frequently form and intensify (Bracegirdle & Gray, 2009;Dierer & Schluenzen, 2005). There is also a two-way interaction of the polar low-level and the upper-level trough. ...
We use a global 5‐km resolution model to analyze the air‐sea interactions during a katabatic storm in the Irminger Sea originating from the Ammassalik valleys. Katabatic storms have not yet been resolved in global climate models, raising the question of whether and how they modify water masses in the Irminger Sea. Our results show that dense water forms along the boundary current and on the shelf during the katabatic storm due to the heat loss caused by the high wind speeds and the strong temperature contrast. The dense water contributes to the lightest upper North Atlantic Deep Water as upper Irminger Sea Intermediate Water and thus to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). The katabatic storm triggers a polar low, which in turn amplifies the near‐surface wind speed due to the superimposed pressure gradient, in addition to acceleration from a breaking mountain wave. Overall, katabatic storms account for up to 25% of the total heat loss (20 January 2020 to 30 September 2021) over the Irminger shelf of the Ammassalik area. Resolving katabatic storms in global models is therefore important for the formation of dense water in the western boundary current of the Irminger Sea, which is relevant to the AMOC, and for the large‐scale atmospheric circulation by triggering polar lows.
... METRAS ist zur Prüfung der implementierten numerischen Verfahren mit analytischen Lösun gen und zur weiteren Validierung mit Messungen und Ergebnissen anderer mesoskaliger Modelle verglichen worden (Bigalke, 1992;Dierer & Schluenzen, 2005;Grawe et al., 2013;Lüpkes et al., 2012;Ries et al., 2010;Schlünzen, 1992;Thunis et al., 2003). Die bei den Modellrechnungen genutzten Parametrisierungen und numerischen Methoden wurden detailliert untersucht (Lüpkes & Schlünzen, 1996;Schlünzen & Katzfey, 2003;Schroeder et al., 2006;Von Salzen et al., 1996;Schroeder et al., 2005;Augustin et al., 2008;Bohnenstengel & Schlünzen, 2009;Schroeder & Schlünzen, 2006;Schlünzen et al., 2011). ...
... The mesoscale transport and fluid model METRAS (Schlünzen, 1990;Lüpkes and Schlünzen, 1996) is a three-dimensional non-hydrostatic mesoscale numerical atmospheric model. It has been previously applied to Germany (Schlünzen, 1992;Renner and Münzenberg, 2003;Schlünzen and Katzfey, 2003;Schüler and Schlünzen, 2006;Schlünzen and Meyer, 2007;Bohnenstengel, 2011, Buschbom et al., 2012, Spain (Augustin et al., 2008), China (Wu and Schlünzen, 1992;Sheng et al., 2000), coastal areas (Niemeier and Schlünzen, 1993;Boettcher et al., 2015), the Arctic (Dierer and Schlünzen, 2005;Hebbinghaus et al., 2007;Lüpkes et al., 2008;Ries et al., 2010) and the urban climate of London (Thompson, 2008;Grawe et al., 2012) with horizontal resolutions ranging from 1 km to 18 km. A detailed description of METRAS is given in Schlünzen et al. (2012a). ...
Regional climate models provide climate projections on a horizontal resolution in the order of 10 km. This is too coarse to sufficiently simulate urban climate related phenomena such as the urban heat island (UHI). Therefore, regional climate projections need to be downscaled. A statistical-dynamical method for the UHI was developed and applied to provide urban climate results at a high resolution with little computational costs. For the downscaling, weather situations relevant for the UHI are determined. This is done by combining objective weather pattern classification based on a k-means cluster analysis of ERA-40 reanalysis data and a regression-based statistical model of the observed UHI of Hamburg. The resulting days for each weather pattern are simulated with the mesoscale meteorological model METRAS at 1 km horizontal resolution. To obtain the average UHI for a climate period, the mesoscale model results are statistically recombined weighted by the frequency of the corresponding weather patterns. This is done for present-day climate (1971–2000) using reanalysis data to yield the current climate UHI. For the future climate periods 2036–2065 and 2070–2099 the results of regional climate projections are employed. Results are presented for Hamburg (Germany). The present day UHI pattern is well reproduced compared to temperature data based on floristic mapping data. The magnitude of the early night-time UHI is underestimated when compared to observed minimum temperature differences. The future UHI pattern does only slightly change towards the end of the 21st century based on A1B scenario results of the RCMs REMO and CLM. However, for CLM the number of days with high UHI intensities significantly increases mainly due to a decrease in near-surface relative humidity.
... MIZ parameters such as its position, width, configuration, and mesoscale circulations in the ocean in the MIZ area are determined in many respects by interaction with the atmosphere (Guest et al., 1995). The position and configuration, in turn, influence the CAO large scale parameters (Pagowski and Moore, 2001) and the creation of MCs (Heine mann, 1996;Dierer and Schluenzen, 2005), while small scale inhomogeneities impact the values of the heat and momentum fluxes within the MIZ (Lüpkes and Birnbaum, 2005), as well as the organization of convection into rolls over the ocean . ...
A review of the current state of research in the field of numerical modelling and forecasting of cold-air outbreaks over the ocean at high latitudes and associated mesoscale circulations is presented. It is shown that the most relevant tasks are as follows: (1) the improvement of predictability and the adequacy of reproduction of polar mesocyclones, (2) a more adequate representation of the marginal sea-ice zone in the numerical models, and (3) solving problems of the parametrization and explicit reproduction of organized convection and orographic jets in numerical atmosphere models. It is demonstrated that these tasks only can be accomplished as a result of a comprehensive development of different components of the climatic system models and technology of the numerical weather prediction (NWP). One of the most promising approaches to overcome the identified problems is to develop and use methods of satellite remote sensing of the atmosphere and underlying surface in NWP technology. The high potential of analyzing the satellite multisensor data for quantifying parameters of different-scale atmospheric circulations is demonstrated using the example of cold-air outbreaks over the seas of the Far East.
... The mesoscale transport and fluid model METRAS (Schlünzen, 1990;Lüpkes and Schlünzen, 1996) is a three-dimensional non-hydrostatic mesoscale numerical atmospheric model. It has been previously applied to Germany (Schlünzen, 1992;Renner and Münzenberg, 2003;Schlünzen and Katzfey, 2003;Schüler and Schlünzen, 2006;Schlünzen and Meyer, 2007;Bohnenstengel, 2011, Buschbom et al., 2012, Spain (Augustin et al., 2008), China (Wu and Schlünzen, 1992;Sheng et al., 2000), coastal areas (Niemeier and Schlünzen, 1993), the Arctic (Dierer and Schlünzen, 2005;Hebbinghaus et al., 2007;Lüpkes et al., 2008;Ries et al., 2010), and the urban climate of London (Thompson, 2008;Grawe et al., 2012 submitted) with horizontal resolutions ranging from 1 km to 18 km. A detailed description of METRAS is given in Schlünzen et al. (2012a). ...
In the present study, the influence of climate change on the urban heat island (UHI) of Hamburg is investigated. Two different methods to downscale regional climate projections with respect to the Hamburg’s UHI are developed. First, a statistical model for the UHI of Hamburg is constructed using observations from the German Meteorological Service (Deutscher Wetterdienst (DWD)). This statistical model explains up to 42% of the UHI variance. By applying it to regional climate projections from REMO and CLM, which were driven with the A1B SRES emission scenario runs from ECHAM5/MPIOM, future changes in the UHI intensity are investigated. The results differ between both RCMs. Except for April and December (which shows a decrease) REMO results show no significant changes to monthly average UHI intensity at the end of the 21st century, while analyses of CLM results show significant decreases from November through April and significant increases in July and August. The frequency distribution of the summer UHI shows no significant changes for REMO and in only one realization of CLM can a significant increase in moderate and strong UHI days be found for the end of the 21st century.
The second downscaling method is based on the concept of statisticaldynamical downscaling (SDD). As a part of the developed SDD method relevant weather situations for the UHI are determined. For this purpose an objective weather pattern classification (WPC) is constructed by applying a k-means based clustering technique to 700 hPa fields (geopotential height, relative humidity, relative vorticity, and thickness) from the ERA40 reanalysis dataset. Changes in the weather pattern (WP) frequencies in a future climate are obtained by applying different RCM results to the WPs. Both REMO and CLM show significant changes the WP-frequencies, especially by the end of the 21st century. Because the constructed WPC does not explain enough of the UHI variance to identify relevant days, it is combined with the statistical UHI model. The resulting relevant days are simulated with the mesoscale numerical model METRAS. In a two-step nesting a resolution of 1 km is reached, forced by ECMWF (European Center for Medium Range Weather Forecasts) analyses data. The UHI patterns obtained for each of the relevant days are then statistically recombined to compute the average pattern for days with a strong UHI (statistically modeled UHI ≥ 3 K). The statistically recombined UHI pattern for the present climate is quite well represented when compared with the available observations. The maximum UHI intensity of 1.2 K is found in the downtown and harbor area of Hamburg.
For the future UHI the SDD method is applied to results from A1B projections conducted with REMO and CLM as well as one A2 projection conducted with the high-resolution global model CCAM. Again, the results differ between the models. The pattern of the strong UHI remains unchanged for REMO while both CLM and CCAM show increases of approximately 0.13 K (some 10% of the simulated maximum UHI intensity) at the end of the century. The changes in CLM and CCAM are associated with a significant increase in strong UHI days.
... The mesoscale transport and fluid model METRAS (Schlünzen, 1990;Lüpkes and Schlünzen, 1996) is a three-dimensional non-hydrostatic mesoscale numerical atmospheric model. It has been previously applied to Germany (Schlünzen, 1992;Renner and Münzenberg, 2003;Schlünzen and Katzfey, 2003;Schüler and Schlünzen, 2006;Schlünzen and Meyer, 2007;Bohnenstengel, 2011, Buschbom et al., 2012, Spain (Augustin et al., 2008), China (Wu and Schlünzen, 1992;Sheng et al., 2000), coastal areas (Niemeier and Schlünzen, 1993;Boettcher et al., 2015), the Arctic (Dierer and Schlünzen, 2005;Hebbinghaus et al., 2007;Lüpkes et al., 2008;Ries et al., 2010) and the urban climate of London (Thompson, 2008;Grawe et al., 2012) with horizontal resolutions ranging from 1 km to 18 km. A detailed description of METRAS is given in Schlünzen et al. (2012a). ...
The European Union has established a 2 K warming of average annual
global surface temperature above pre-industrial levels as a target to
avoid disruptive climate change. The Hamburg 2K project seeks to model
the climate of Hamburg, Germany subject to this target warming by the
end of the 21st century. A general circulation model (ECHAM5) with a
greenhouse gas scenario consistent with this target (E1) provides a
source for dynamical and statistical-dynamical model downscaling at the
regional scale, using the Regional Model (REMO), and at the mesoscale,
using the Mesoscale Transport and fluid (Stream) Model (METRAS).
Regional scale model estimates provide forcing for off-line modeling of
the North Sea circulation with the Hamburg Shelf-Ocean Model (HAMSOM).
This presentation concentrates on the urban climate component of the 2K
scenario. The approach quantifies the projected change in both the
meteorology and the urban development. The modeling strategy allows for
a discrete diagnosis of each contribution. For the meteorology, the
project identifies an urban climate change signal between the late 20th
and late 21st centuries using a statistical-dynamical downscaling
technique. Cluster analysis of multiple REMO realizations generates a
series of archetypical synoptic conditions, a.k.a., weather types. The
frequency change of these weather types between present and future
climate yields a climate change signal. The potential for distinctively
new weather types in the future climate is also investigated. Regional
weather types provide the forcing for simulations with METRAS at 1 km
resolution. These simulations provide further assessment of urban
climate change at a scale more sensitive to the heterogeneous urban
surface. Some initial METRAS modeling results will be presented here.
For the urban development, the METRAS model simulations benefit from a
detailed surface cover map including over 50 classes of natural and
artificial surfaces tailored specifically for Hamburg. The simulations
of future climate incorporate estimates of future surface cover.
Evaluation of current municipal construction plans helps quantify trends
in building density and change in unsealed surface cover. An off-line
urban planning model tuned for the 2K scenario incorporates these plans
into its parameterizations and assists in deriving a future surface
cover map of Hamburg.
... The mesoscale transport and fluid model METRAS (Schlünzen, 1990;Lüpkes and Schlünzen, 1996) is a three-dimensional non-hydrostatic mesoscale numerical atmospheric model. It has been previously applied to Germany (Schlünzen, 1992;Renner and Münzenberg, 2003;Schlünzen and Katzfey, 2003;Schüler and Schlünzen, 2006;Schlünzen and Meyer, 2007;Bohnenstengel, 2011, Buschbom et al., 2012, Spain (Augustin et al., 2008), China (Wu and Schlünzen, 1992;Sheng et al., 2000), coastal areas (Niemeier and Schlünzen, 1993;Boettcher et al., 2015), the Arctic (Dierer and Schlünzen, 2005;Hebbinghaus et al., 2007;Lüpkes et al., 2008;Ries et al., 2010) and the urban climate of London (Thompson, 2008;Grawe et al., 2012) with horizontal resolutions ranging from 1 km to 18 km. A detailed description of METRAS is given in Schlünzen et al. (2012a). ...
In the framework of the interdisciplinary project KLIMZUG-NORD,
adaptation measures to climate change are developed for the Metropolitan
Region of Hamburg. For the development of these measures it is crucial
to know how the urban climate of Hamburg, a city with a population of
1.8 Mio, will alter due to climate change. Regional climate models
provide climate projections on a horizontal resolution of up to 10 km,
which is still too coarse to sufficiently simulate urban related
phenomena such as the urban heat island (UHI). Therefore, these climate
projections have to be downscaled. Since the computational amount
increases rapidly with increasing horizontal resolution, a
statistical-dynamical method for the UHI was developed. As a first step
of the downscaling method, synoptic situations which are relevant for
the UHI are determined. This is done combining objective weather type
classification of ERA-40 reanalysis data using k-means-based cluster
analysis and a regression-based statistical model for the observed UHI
of Hamburg. The meteorological variables and domain used for the weather
type classification are chosen to explain the variability of the UHI as
best as possible. The second step is the simulation of the resulting
synoptic situations with the mesoscale meteorological model METRAS
providing a horizontal resolution of 1 km. To get the average UHI for a
certain period, the simulation results are statistically recombined
according to the frequency of the synoptic weather types. This is done
for present and future climate simulations for the A1B scenario
conducted with the regional climate models REMO and CLM and for the A2
scenario conducted with the regional climate model CCAM to identify
changes in Hamburg's UHI. In this presentation the method will be
presented with focus on the weather type classification and on the
simulation results for the summer season.
... This large variability is mainly due to synoptic scale and mesoscale disturbances passing through the Fram Strait. The development of these atmospheric disturbances is influenced by the sea-ice characteristics (Dierer and Schlünzen, 2005). Via turbulent momentum-and heat fluxes mesoscale structures like fronts and polar cyclones are linked to surface characteristics such as roughness or sea-ice distribution. ...
... Valkonen et al. (2008) found the sea-ice concentration to play an important role for the near-ground temperature and wind field during a study in the Weddell Sea. For the simulation of a mesoscale cyclone passage with dynamic changes in the sea-ice distribution, a strong influence on the heat fluxes has been found when compared to simulations with constant sea-ice distribution (Dierer and Schlünzen, 2005). Here the development of an on-ice moving trough in the Fram Strait on 7 March 2002 is investigated. ...
... The simulations are performed with the mesoscale transport and fluid model METRAS (Schlünzen, 1990; Lüpkes and Schlünzen, 1996). Parametrization options that have been proven to deliver most realistic results for high latitude applications have been chosen (Lüpkes and Birnbaum, 2005; Dierer et al., 2005). The model treats the sea ice as invariant with respect to position and the characteristics mentioned (except sea-ice temperature). ...
The impacts of the sea-ice characteristics distribution, roughness, temperature and thermal conductivity on an on-ice moving trough in the Fram Strait on 7 March 2002 are investigated. The situation is simulated with the mesoscale transport and fluid model METRAS and the named characteristics are varied within the range of observational uncertainty. The test cases are evaluated against aircraft measurements performed within the 'Fram Strait Cyclone Experiment 2002'. The model's sensitivity on the changes in sea-ice characteristics is quantified by statistical means. The strongest impacts on the near-ground temperature are found from sea-ice temperature, manifesting as an overall bias, and the positioning of the sea-ice edge, manifesting as a phase error. Only higher than natural homogenization of the sea-ice cover leads to some reduction of the amplitude error. A reduction of the sea-ice surface roughness is performed by applying an unrealistically small roughness length of ! z(0) = 1 mm. This reduces the negative wind speed bias, enhances the advection of contrasting air masses and improves the frontal sharpness. The thermal conductivity has the smallest influence. The lateral forcing taken from 'European Centre for Medium-Range Weather Forecasts' (ECMWF) reanalyses shows the strongest effect on the limited area model performance.
... In this study, the building energy parameterisation BEP (Martilli et al., 2002) has been implemented into the mesoscale meteorology model METRAS (Dierer and Schlünzen, 2005;Schlünzen, 1990) in order to investigate the urban climate of London, UK. Initial results are presented for an idealised domain as well as for a realistic domain covering the area of Greater London. ...
The mesoscale meteorology model METRAS has been coupled to the urban canopy scheme BEP (Building Energy Parameterisation) and the revised model has been applied to different domains for evaluation. First results for an idealised domain show increased urban temperatures (urban heat island), especially at night and a more pronounced urban boundary layer during daytime. Results for a realistic domain for the urban area of London, UK show that the combined model results provide a better simulation of actual measurements for daytime as well as night time tem-peratures.
In this study, a new multilayer urban canopy parameterization for high‐resolution (∼1 km) atmospheric models using the nudging approach to represent the impacts of urban canopies on airflow is presented. In our parameterization, a nudging term is added to the momentum equations and a source term to the turbulent kinetic energy equation to account for building effects. The challenge of this parameterization lies in defining appropriate values for the nudging coefficient and the weighting function used to reflect canopy effects. Values of both are derived and the parameterization developed is implemented and tested for idealized cases in the Mesoscale Transport and Stream model (METRAS). Comparison data are taken from obstacle‐resolving microscale model results. Results show that the parameterization using the nudging approach can simulate aerodynamic effects induced within the canopy by obstacles well, in terms of reduction of wind speeds and production of additional turbulent kinetic energy. Thus, models with existing nudging can use this approach as an efficient and effective method to parameterize dynamic urban canopy effects.
