ISSN 1006-9895

CN 11-1768/O4

Key Circulation Characteristics of Spring-to-summer Seasonal Transition Process over the Mid- and High Latitude Asia

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    The spring-to-summer seasonal transition over the Mid- and High Latitude Asia (MHASST) is an important part of the several spring-to-summer seasonal transitions in different regions of the Asian continent. It provides the necessary circulation conditions in the mid- and high latitudes for the establishment of the Meiyu rainfall in the Yangtze and Huaihe River basins. However, so far there is no systematic summary on its uniqueness and key characteristics. In this paper, we analyze and summarize the key characteristics of the MHASST process, based on the daily data of NCEP / NCAR reanalysis data I. The MHASST is symbolized by the establishment of the Northeast Asian ridge at 500 hPa and then the "double blocking" circulation pattern. The formation of the Northeast Asian ridge and its related land sea temperature difference is mainly attributed to the snow melting process and thus the local strong warming process in Northeast Asia. The establishment of the northern East Asian low (850 hPa) is another important sign of the MHASST. When the MHASST occurs, the 200 hPa Asian jet axis over the Tibetan Plateau jumps northward from ~ 35oN to ~ 37oN, while the Asian temperate jet disappears completely. With the seasonal change, the meridional gradient of near surface temperature in the mid- and high latitude Asia weakens, thus causing the attenuation of high frequency transient baroclinic disturbances. In contrast, low-frequency weather systems, including the Asian Blocking high and the northeast China cold vortex system, become the dominant weather systems in the same region. From the perspective of the early and late timing of the MHASST, this paper also discusses the evolution features of the circulation and weather system over the mid- and high latitude Asia, and the results further supplement the key information of the climatic MHASST.

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  • Received:February 06,2021
  • Revised:April 28,2021
  • Adopted:May 06,2021
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