Abstract
The results of numerical simulations aimed at dynamic downscaling the ERA-Interim reanalysis data for the Black Sea-Caspian region using the RegCM4 climate model are described. The downscaling results in reconstruction of the atmospheric circulation fields in the region with the increased spatial resolution (25x25 km) for 1979-2013. The modeling results are compared with the original largescale fields with the purpose to validate the regional model. The analysis shows that the model correctly reproduces climate in the region; at that original integral climatic characteristics are retained. Realistic annual cycle and seasonal spatial distribution of main meteorological parameters (temperature, precipitation and wind circulation) are obtained by the model simulations. However, the following discrepancies are found.
In the northern part of the region summer air temperature is overestimated by 1.5-2 degrees C. This effect is observed in the flat areas and it does not related to the model orography differences. Probably, overestimation of summer temperature is related to disadvantages of cloud cover parameterization schemes and inaccuracies of radiation calculation. In favor of this assumption comes underestimation of summer precipitation amount in the northern areas of the domain.
Overestimated (by 25-30 %) precipitation in the autumn-winter period and the heightened (by 1.5-2 degrees C) air temperature in summer are noted in the northern part of the region. Further analysis shows that the increased precipitation is, mainly, a result of overestimating its intensity, whereas the simulated precipitation frequency approximates the original data. Precipitation intensity according to regional model data significantly exceeds the one obtained according to reanalysis data during the entire year. In the cold season this is related to more intensive large-scale (non-convective) precipitation prevailing in this period.
Hence, the scheme of precipitation parameterization requires optimization.