ISSN 1006-9895

CN 11-1768/O4

Relationship between two types of east-west oscillation of the South Asian High and their different influences on weather
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Institute of Atmospheric Physics, Chinese Academy of Sciences

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    Abstract:

    The South Asian high (SAH) center is characterized by bimodality distribution (i.e., Tibetan Plateau (TP) mode and Iranian Plateau (IP) mode), showing an east-west oscillation pattern. In addition, east edge of the SAH also regularly extends eastward to East Asia or retreats westward to the TP, manifesting another type of east-west oscillation. By using NCEP1 daily reanalysis data, APHRODITE daily precipitation data and daily precipitation data in India, this paper investigates the relationship between the two types of east-west oscillation of the SAH, and the differences in their impacts on the circulation and weather in Asia. The results show that bimodality east-west oscillation of the SAH center can significantly affect the occurrence and amplitude of eastward extension/westward retreat of the east edge of the SAH. Although the east edge of the SAH can extends eastward when the SAH center is in the TP or IP mode, the frequency of eastward extension of the east edge of the SAH in the TP mode is significantly higher than that in the IP mode; In the IP mode, east edge of the SAH is more prone to retreat westward. And magnitude of eastward extension of the east edge of the SAH in the TP mode is larger than that in the IP mode. Further analysis reveals that bimodality east-west oscillation of the SAH center is closely related to the rainfall anomaly pattern in the northern India and the TP region, and is coupled with the variation of thermodynamic effect related to rainfall anomaly. While the eastward extension/westward retreat of the east edge of the SAH is related to the dipole rainfall anomaly pattern in East Asia (i.e., rainfall anomaly in the central and eastern TP, and in the middle and lower reaches of the Yangtze River and Yellow river, is opposite to that in the region south of the Yangtze river), by resulting in the westward extension/eastward retreat of the western Pacific subtropical high. Furthermore, when the SAH is in the TP mode and its east edge extends eastward, and when the SAH is in the IP mode and its east edge retreats westward, rainfall anomaly in the western TP is always opposite to that in the central and eastern TP.

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History
  • Received:April 30,2021
  • Revised:June 09,2021
  • Adopted:July 05,2021
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