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Sensitivity of a high-resolution RCM to land-surface forcing in representing land-atmosphere feedbacks 

Conference: Latsis Symposium 2019
Year: 2019
Contribution type: Submitted
, Goergen, K., , Warach-Sagi, K., , Ingwersen,J., Wulfmeyer, V.

Continuous increase in computational resources allows for regional climate models (RCMs) to run at convection permitting (CP) scale, where deep convection is explicitly resolved and not parameterized. Convection parametrizations have a strong influence on precipitation uncertainty in coarser climate simulations, also increasing inter-model variability. Therefore, CP-RCMs are expected to better represent precipitation climatology, with special emphasis on extreme events related to convective processes. For the first time, a multi-model ensemble of such high-resolution RCMs over the Mediterranean is being produced within the framework of the international CORDEX - Flagship Pilot Study on Convective phenomena at high resolution over Europe and the Mediterranean (FPS-CEM).
As model resolution increases, accuracy and resolution of input information, such as land use and soil texture, become more important. Quality of these data may have a strong impact not only on surface fluxes, but also on the representation of boundary layer evolution and precipitation, which depends on the strength of the land-atmosphere coupling.
In this work, we used the Weather Research and Forecasting (WRF) model, where this static information is, by default, based on MODIS land use and FAO soil texture. We adapted higher resolution and up-to-date data sets for WRF, based on CORINE (at 100 m resolution) for land use and on HWSD and BÜK databases (at 1 km resolution) for top soil texture data. These new static data have been used by all WRF groups involved in the FPS-CEM.
We extended the case-study experimental design of the FPS-CEM (Coppola et al. 2018) to include the WRF sensitivity to these available static data. For this experiment, we generated two 8-member ensembles, one for a summer and one for a winter case. The two cases resemble the two test cases (Austria and Foehn case) conducted in climate mode (~1 month long). For each case, 4 simulations differing in combinations of the static data have been conducted twice, with different physical parameterization settings.
In this study we focus on representation of land-surface-atmosphere (LA) feedback processes over the Alpine domain on CP scale, and its sensitivity to (1) land-surface static forcing, (2) season, and (3) WRF configuration. To quantify the strength of LA coupling for each grid, we use coupling metrics appropriate for relatively short time scales, such as mixing diagram. Furthermore, we explore the impact of land-surface changes on the potential for convection and precipitation occurrence.