About low-frequency change of wind fields and geostrophic flows of the Black Sea on satellite data. Part 1: Season cycle

A.B. Polonsky1,2,3, A.N. Serebrennikov1

1Institute of Natural and Technical Systems, RF, Sevastopol

E-mail: apolonsky5@mail.ru; swsilv@gmail.com

2Branch of Moscow State University in Sevastopol, RF, Sevastopol

3Sevastopol State University, RF, Sevastopol

DOI: 10.33075/2220-5861-2019-2-64-72

UDC 551.465.7

Abstract: 

   The seasonal variability of the surface wind and its vorticity associated with the lateral shift, as well as the seasonal variability of geostrophic currents for the Black Sea were studied on the basis of daily satellite information on the surface wind for 1988–2017 and sea surface level anomalies for 1993–2017.

   The northern winds dominate the Black Sea area on average. Wind vectors over the southwestern part of the water area are twisted in the western direction, while over the southeastern part – in the eastern one. Thus, modern climatic wind over the sea is characterized by cyclonic vorticity in the eastern part of the region and anticyclonic in the western part. Maximum climatic wind speeds are confined to the western part of the water area. Analysis of the average climatic fields of the vorticity of the wind field for each month shows mainly cyclonic vorticity from October to March. Anticyclonic vorticity, by contrast, prevails from July to September.

   The map of average climatic anomalies of geostrophic currents, built over the entire study period, indicates predominantly cyclonic vorticity of large-scale currents in the Black Sea, forming a cyclonic circulation, with two sub-basin structures (so-called Knipovich glasses). Monthly analysis of average climatic fields of geostrophic current anomalies shows that the cyclonic vorticity of large-scale gyres prevails for 6 months: from November to April. Anticyclonic vorticity, on the contrary, prevails from May to October. The strongest eddy current in the southeastern region of the Black Sea, which coincides in direction with the large-scale gyre, strengthens (in the cyclonic direction) or weakens the Main Black Sea Current.

Keywords: near-surface wind, geostrophic current, Ekman pumping, wind vorticity.

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