A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period

A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using simi lar surface and lateral boundary conditions, and ran in either data assimil ation mode (short term forecasts plus data assimilation), forecast made (sh ort term forecasts initialised daily with analyses) or climate mode (no re- initialisation of model interior during entire simulation period). Model re sults presented in this paper were generally post processed as daily averag ed quantities, separate for land and sea areas when relevant. Post processe d output was compared against available analyses or observations of cloud c over, precipitation, vertically integrated atmospheric specific humidity, r unoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degr ee of agreement among the participating model results for most cases. Model s operated in climate mode generally displayed slightly larger deviations f rom the observations than the data assimilation or forecast mode integratio n, but in all cases synoptic events were well captured. Correspondence to n ear surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative pro perties, average precipitation and runoff. Problems with choosing appropria te initial soil moisture conditions from a common initial soil moisture fie ld resulted in a wide range of evaporation and sensible heat flux values du ring the first few weeks of the simulations, but better agreement was shown at later times.