A shallow, short-lived meso-β cyclone over the Gulf of Antalya, eastern Mediterranean

Abstract

The physical mechanisms of a shallow short-lived meso-β scale cyclone over the Gulf ofAntalya, eastern Mediterranean, are studied, with the PSU/NCAR MM4 and MM5 mesoscalemodels. Although the thin stratus clouds within this cyclone as observed from satellitesare not resolved even by the 3 km nesting, the dynamical evolution and the 3-D structureare well captured. The small cyclone or eddy develops before sunrise following convergenceof the strong katabatic winds from the nearby steep Anatolya mountains slopes with 2 kmpeaks. The eddy’s lifetime is of the order of 5–7 h and it quickly dissipates before noon. Based on the simulated vertical winds, vorticity, humidity as well as the IR top cloudtemperatures, the depth of the eddy is estimated to be 500–800 m. It is shown that thedivergence term in the vorticity equation is dominant during the eddy’s generation.Lagrangian analysis for the trajectories of several air-masses that were identified as crucialfor the eddy’s development, reveals a sharp increase both in the PV (by 7–8 units), and inthe specific humidity, 3.5 to 7 g/kg, as the air-parcels descend from about 840 to 980 hPa. This air-parcel analysis also shows that the diabatic contribution is quite important. Factorseparation experiments confirm that pure topography is the major factor and the synergisticeffect of sea-fluxes and topography contributes about 20% of the total vorticity. The Antalyacyclone is common during July to September morning hours and its frequency of occurrencewas estimated from satellite pictures to be about 20%.