Effects of different initial and boundary conditions in ALADIN/HR simulations during MAP IOPs

Abstract

In order to better understand the influence of initial and boundary conditions on the numerical model results for MAP IOP5 (heavy precipitation) and IOP15 (severe Bora wind), numerical experiments were performed using the operational ALADIN/HR (hydrostatic) limited area model. Three experiments were performed. For the reference experiment (ARPE), ARPEGE operational analyses from 1999 were used. The other two experiments (ECAR and ECMW) were initialized from the 4D-Var ECMWF MAP reanalysis. In ECAR, the surface analysis was used from ARPEGE. The results presented here emphasise the huge importance of initial low-level moisture for the convective precipitation during IOP5. The humidity distribution in the ECMW experiment shows predominantly more humid conditions over the Dinaric Alps than in ARPE and ECAR. As a result, the simulation based upon the ECMWF MAP reanalysis produces fairly realistic results. The intensive surface convergence in the wind field and the orographic lifting of warm and humid air from the Adriatic Sea resulted in heavy precipitation in western Croatia. On the other hand, the different initial conditions during the MAP IOP15, with respect to the wind fields only, do not have a significant influence.