Climatology of Polar Mesocyclones over the Sea of Japan Using a New Objective Tracking Method

Abstract

olar mesocyclones (PMCs) are mesoscale cyclonic vortices that develop poleward of the main polar front. This article reports on a new algorithm for the objective tracking of PMCs, including meso-?-scale vortices, which will facilitate the study of their climatology. The algorithm is based mainly on the vorticity field and consists of three parts: the identification of vortices, the connection of vortices at consecutive time steps, and discrimination between PMCs and synoptic-scale disturbances. The objective tracking method was applied to Mesoscale Analysis (MA) data provided by the Japan Meteorological Agency, which has a horizontal resolution of 5 km. The detected tracks of PMCs were confirmed by subjective analysis of the MA data and satellite images. The method used here to discriminate between PMCs and synoptic-scale disturbances differs from that used in previous studies, which is based on the difference between the sea surface temperature and the temperature at 500 hPa, but gives a consistent result. This objective tracking method was used to obtain the climatology of PMCs over the Sea of Japan, which were classified into three groups according to the regions where they attained their maximum intensity. In each region, the PMCs have different characteristics with respect to their direction of movement, size, and intensity, which are likely to be related to their environment or development mechanism.