Comparison of the Synoptic Environment and Mechanisms of Two Cases of Surface Cyclogenesis in Greek Area Associated to Strong Low-Level Cold Surges

Abstract

In this study the synoptic environment and thermodynamic mechanisms of two cases of surface cyclogenesis in the south Ionian and Aegean Seas, associated to strong low-level cold surges, are analyzed. The cases are characteristic examples of two different synoptic categories, affecting the weather in the Greek area. The analysis was performed using the ERA-Interim dataset on a 0.5° × 0.5° regular latitude-longitude grid. In the first case, the passage of a frontal depression from North Greece caused the extension of a cold anticyclone from NW Europe towards Greece. Then, the formation of a surface frontal depression is triggered over the south Ionian Sea. In the second case, the eastward movement of a strong frontal depression from North Europe along with a secondary frontogenesis in East Europe favored surface cyclogenesis over the north Aegean Sea. The depression propagated towards the south Aegean Sea, combined with the extension of a cold anticyclone over the Balkans. Although upper-level baroclinic processes significantly affected the formation of the surface depressions in both cases, the two cases are characterized by differences at the low levels, i.e. strengthening of low-level baroclinicity and convergence in the first case and low-level cold advection from the north in the second.