On a space-time variability and trends of wind stress curl over the Black Sea

by

E.A. Averyanova, A.V. Gubarev, A.B. Polonsky

Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28

E-mail: eisal@mail.ru, alexgub@inbox.ru, apolonsky5@mail.ru

DOI: 10.33075/2220-5861-2020-1-27-36

UDC 551.553, 551.465.7

Abstract:

    Spatiotemporal variability of wind stress curl over the Black Sea for the period 1980-2018 and linear trends are analyzed, using the data of wind speed from four re-analyses (NCEP-DOE, ERA-Interim, MERRA2, JRA-55). The best agreement between the spatial structures of standard deviation (STD) fields due to interannual variability of wind stress curl (WSC) is found for MERRA2 and ERA-Interim re-analyses. The maximum interannual variability of WSC is located near the coast of Turkey (30 ° ÷ 35 ° E), while the minimum corresponds to Batumi quasistationary anticyclone eddy. Typical STD values of annual mean WSC, averaged over the Black Sea area, slightly differ from each other according to MERRA2, ERA-Interim, and JRA-55 data. These values vary between 9,11⋅10-9 Pa/м and 9,53⋅10-9 Pa/м. Spatial structure of linear trend fields of annual mean WSC values obtained from ERA-Interim and MERRA2 data is characterized by the following similar features:  positive significant trends of WSC correspond to the regions of the western and eastern cyclonic gyres, as well as to the coastal zone near the Bosphorus and the Kerch Strait. Negative significant WSC trend areas are located near the Caucasus coast, and near the shores of Turkey (31 ° ÷ 34 ° E).

     Averaged over the Black Sea mean annual values of WSC for the period 1980–2018 are characterized by significant positive trends according to MERRA2, ERA-Interim. Trends calculated from NCEP-DOE and JRA-55 data are not statistically significant. So, most likely, an increase in cyclonic vorticity, occurred over the Black Sea during the studied period, should cause an intensification of water circulation in the sea.

Keywords: Black Sea, wind stress curl, atmospheric re-analyses, interannual variability, trends.

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