A shallow, short-lived meso-beta cyclone over the Gulf of Antalya, easternMediterranean

The physical mechanisms of a shallow short-lived meso-beta scale cyclone ov er the Gulf of Antalya, eastern Mediterranean, are studied, with the PSU/NC AR MM4 and MM5 mesoscale models. Although the thin stratus clouds within th is cyclone as observed from satellites are not resolved even by the 3 km ne sting, the dynamical evolution and the 3-D structure are well captured. The small cyclone or eddy develops before sunrise following convergence of the strong katabatic winds from the nearby steep Anatolya mountains slopes wit h 2 km peaks. The eddy's lifetime is of the order of 5-7 h and it quickly d issipates before noon. Based on the simulated vertical winds, vorticity, hu midity as well as the IR top cloud temperatures, the depth of the eddy is e stimated to be 500-800 m. It is shown that the divergence term in the vorti city equation is dominant during the eddy's generation. Lagrangian analysis for the trajectories of several air-masses that were identified as crucial for the eddy's development, reveals a sharp increase both in the PV (by 7- 8 units), and in the specific humidity, 3.5 to 7 g/kg, as the air-parcels d escend from about 840 to 980 hPa. This air-parcel analysis also shows that the diabatic contribution is quite important. Factor separation experiments confirm that pure topography is the major factor and the synergistic effec t of sea-fluxes and topography contributes about 20% of the total vorticity . The Antalya cyclone is common during July to September morning hours and its frequency of occurrence was estimated from satellite pictures to be abo ut 20%.