Mesoscale Eddies of the Baltic Sea according to the Physical Reanalysis

The mesoscale eddies of the Baltic Sea are analyzed based on the algorithm for automatic identification of eddies and the BALTICSEA_REANALYSIS_PHY_003_011 data. It is shown that most of mesoscale eddies have an amplitude (a level difference from the center to the boundary of an eddy) of 0.05–0.20 m, a radius of 5–10 km, and a lifetime of 2–3 days. From 1993 to 2020, 120000 eddies were detected, the number of cyclones exceeded the number of anticyclones, and anticyclones had a larger radius, geostrophic velocity, and lifetime. On average, Baltic eddies have a geostrophic velocity of about 6.5 cm/s and move for 4 km per day. The concentration areas of eddies have been detected for cyclones and anticyclones, and their general circulation has been also shown. Long-lived eddies make up only 1.5% of the total number of eddies, and their movement is highly influenced by topography. The average ratio of the major to minor semi-axes of Baltic eddies is 1.58. Their amplitude is maximal in the autumn-winter period, while their number and radius are maximal in summer. For the amplitude and number of eddies and their area, there are a significant interannual variability and significant linear trends. Eddies on average occupy 2% of the Baltic Sea area in winter and 4% in summer.