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Explicit convection and scale-aware cumulus parameterizations

High-resolution simulations over areas of different topography in Germany
: Wagner, Andreas; Heinzeller, Dominikus; Wagner, Sven; Rummler, Thomas; Kunstmann, Harald


Monthly weather review 146 (2018), Nr.6, S.1925-1944
ISSN: 0027-0644
ISSN: 1520-0493
Bundesministerium für Bildung und Forschung BMBF
Synthetische Niederschlagszeitreihen für die optimale Planung und den Betrieb von Stadtentwässerungssystemen
Fraunhofer IAO ()

An increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection. The present study investigates further potential benefits with respect to precipitation, based on a small ensemble of high-resolution simulations with WRF with grid spacings up to 1 km. The skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern Germany and a mainly flat region in northern Germany. This study allows us to differentiate between the impact of grid spacing, topography, and convection parameterization. Furthermore, the performance of a state-of-the-art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only. Our evaluation demonstrates the following: high-resolution simulations (5 and 1 km) are generally able to represent the diurnal cycle, structure, and intensity distribution of precipitation, when compared to observational datasets such as radar data and interpolated station data. The influence of the improved representation of the topography at higher resolution (1 km) becomes apparent in complex terrain, where the localization of precipitation maxima is more accurate, although these maxima are overestimated. In flat areas, differences in spatial evaluations arise between simulations with parameterized and explicitly calculated convection, whereas smaller grid spacings (1 km vs 5km) show hardly any impact on precipitation results.