engleski

Sensitivity of atmospheric stratification to physical parameterizations in a regional climate model

The heavy precipitation events (HPEs) present a challenge for regional climate models (RCMs) mostly due to parametrised physical processes, especially convection. The aim is to examine the impact of parameters in parameterization schemes on atmospheric stratification in these extreme conditions. We analyse the HPEs during the HyMeX campaign in autumn 2012 that affected the coastal mountainous region of Croatia using the spectrally nudged RCM ALADIN-Climate version 6.3 (ALD6) driven by ERA-Interim reanalysis over the Med-CORDEX domain. Four experiments were conducted for each HPE with parameter changes in physical parameterization schemes, specifically in convection scheme (entrainment and aerodynamical drag), microphysics, radiation, turbulence and dynamics. Temperature and dew temperature vertical profiles from the model were examined and compared with radio sounding data from Zadar. Additionally, the thermodynamic (CAPE, CAPE3, CIN, K-index, LI) and kinematic indices (vertical wind shear) were analysed. For most of the HPEs temperature profiles are close to each other and in good agreement with observations, but humidity profiles, depending on the HPE and atmospheric level, show drier or moister conditions compared to observations. Results for CAPE, CAPE3 and CIN show different discrepancies depending on the HPEs, but none of the experiments missed the event and the results are comparable to observed. Also, it seems that the timing of the maximum values of all of these indices is somewhat shifted compared to the observed maximum. K- index and LI show very similar values to observed and quite small variability between experiments. Results for the vertical wind shear in several layers for all experiments show very good agreement with observed values. Still, more experiments are needed to evaluate and optimize the model performance over such complex terrain.

regional climate model ; CNRM-ALADIN ; physical parameterizations ; atmospheric stratification

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