SIMULATION OF THE WIND-FIELD IN ATHENS USING REFINED BOUNDARY-CONDITIONS

The nested version of the prognostic mesoscale model MEMO was applied in the frame of the APSIS project to simulate air flow in Athens. By performing an additional simulation for an expanded model domain, this version allows imposing numerically computed boundary values at a higher temporal and spatial resolution. This approach is far superior compared to that of the non-nested version of MEMO, in the case of which lateral boundary conditions proved to have a significant influence on the surface how held. In the present paper two days corresponding to two different meteorological situations are considered: 25 May 1990 (APSIS A) and 10 June 1987 (APSIS A'). While the former case is typical for stagnant conditions in Athens, the latter is characteristic for the sea breeze circulation in the area. Simulation results for 10 June 1987 are compared with available measurements. This comparison reveals that MEMO reproduces very satisfactorily the mesoscale dow pattern in Athens. Both investigated synoptic conditions are found to be favourable for the occurrence of air pollution episodes in Athens. Additionally it is proved that mesoscale flow results are rather sensitive to even small changes in large scale environment conditions.