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CN 11-1768/O4

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The Variation of Asian Westerly Jet Asymmetry and Its Impacts on East Asian Climate in Boreal Summer

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    Based on the monthly mean rainfall data of CMAP and reanalysis of NCEP/DOE ⅡReanalysis form NOAA and the monthly precipitation and average temperature data from NMC,by defining an index (IAja) that is defined to describe the zonal asymmetric variation of Asian Westerly jet in upper troposphere, we have investigated the characteristics of the intensity difference between the east and west part of the Asian westerly jet and its climate impacts on East Asia from 1979 to 2019. The main conclusions are as follows: there are prominent inter-annual variations of the zonal asymmetry of Asian summer westerly jet, existing significant quasi-period of 6~8 years and 2 years. When the zonal asymmetry of Asian summer westerly jet is typically strong (weak), the wave-like anomalous rainfall pattern signed with the positive (negative)—negative (positive)—positive (negative) signs is observed form lower to higher latitudes in East Asia sector along with negative (positive) anomalies of temperature in the area of Lake Baikal,and simultaneously significant positive (negative) anomalies in regions including the Western area of China and Northern parts of Japan. The divergent and convergent wind components by the anomalous diabatic heating as a potential vorticity source directly induce the anomalies circulation in the mid-latitudes. The anomalous anticyclonic circulation making the intensity of west Asian jet increased and the eastern segment decreased help to the zonal asymmetry of Asian summer westerly jet stronger. The formation and facilitating of zonal asymmetric anomalies of the Asian jet are affected by not only convergence and divergence in the tropics and mid-latitudes, but also by wave energy propagating eastwards in westerlies. The eastward propagation of wave energy may be related to the SST anomaly of the Northern Atlantic. These results are helpful for us to better understand the formation mechanisms of the zonal asymmetry of Asian summer westerly jet.

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  • Received:October 21,2019
  • Revised:May 10,2020
  • Adopted:June 01,2020
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