Summer atmospheric circulation of the Northern hemisphere in strong and weak East Asian summer monsoon periods
O.Yu. Antokhina1, P.N. Antokhin1, O.S. Kochetkova2, V.I. Mordvinov2
1V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, 1, Academician Zuev square, Tomsk, 634021, Russia
2Institute of Solar-Terrestrial Physics of the Siberian Branch of the RAS, 664033, Irkutsk, 126a, Lermontova str
Keywords: East Asian summer monsoon, general atmospheric circulation, weakening of monsoon, geopotential, wind velocity field, meridional flows, tropospheric trough
Abstract
The composite analysis of average for July pressure and wind fields in the strong and weak East Asian summer monsoon (EASM) periods was carried out using ECMWF ERA–40 and ERA–Interim data. The study showed that the strong EASM periods are characterized by increased meridional flows over East Asia, especially in the area of the monsoon and mid-latitude circulation interaction, where an increased cyclonicity zone appeares. Over large parts of Asia, the atmospheric pressure is higher in the weak EASM periods. In the weak EASM periods, the polar vortex is weak; however, troughs over the Kara Sea, the Sea of Okhotsk, and Hudson Bay are clearly developed. In the Aleutian depression area, the pressure is also reduced. The strongest and most significant long-term changes in the pressure field, indicating weakening of the meridional exchange in recent decades, are characteristic for areas of convergence of the meridional flows of the East Asian and African monsoon.
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