A subsynoptic vortex over the Mediterranean with some resemblance to polar lows

Abstract

The development of a subsynoptic vortex over the Mediterranean has been followed for several days (27 September-1 October 1983). The major tool for the study are METEOSAT images from the visible and infrared spectrum, and wind data from low and high levels obtained by tracking cloud elements in these images. The subsynoptic vortex forms in the central part of a synoptic scale low of modest intensity, and deep convection is observed in the region prior to the formation of the vortex. The initial formation of the vortex is most probably caused by a rapid spin-up due to intense convection of pre-existing vorticity associated with the synoptic scale low. After its formation, the vortex moves in a large circle and is best developed at a position over the sea west of Sardinia and Corsica. The vortex at this time is characterized by deep convection, a vertical axis and an upper-level anticyclonic divergent flow corresponding to a warm core structure.