The long-term variation in the South Asia High intensity measured by 150-hPa eddy geopotential height
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ORIGINAL PAPER
The long‑term variation in the South Asia High intensity measured by 150‑hPa eddy geopotential height Xu Xue1,2 · Wen Chen3 · Shuangshuang Hou1 Received: 3 April 2019 / Accepted: 4 January 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract This study provides some observational evidences to reveal that some discrepancies appear in the long-term variation in the South Asia High (SAH) based on geopotential height field (HGT; termed as HGTSAH), and eddy HGT field calculated as that HGT at each grid is subtracted by the zonal belt mean HGT (EHGT; termed as EDDYSAH). Noticeably increasing trend exists in the HGTSAH intensity and the global mean HGT. The HGTSAH intensity is closely connected to the global mean, which indicates that the increasing trend in the HGTSAH may be forced by the apparent increment of the HGT under the global warming. However, after removing the global mean value, significant weakening trend is observed in the EDDYSAH intensity. Multiple SAH-associated variables such as the horizontal winds and the relative vorticity are thereby examined. The distributions of horizontal winds and relative vorticity are nearly the same as those in the EHGT and eddy tropospheric temperature (ETT) field. Simultaneously, the EDDYSAH is noticeably negatively correlated with the Silk Road pattern (SRP). The SRP shows a noticeably increasing trend, and the SRP-associated cyclonic circulation and negative EHGT over western Asia and southern Tibetan Plateau are preferentially enhanced, which may result in a reduced EDDYSAH. Therefore, via investigating the distributions of the multiple SAH-associated variables, it is found that the variations in the EDDYSAH coincide well with those in the horizontal winds and relative vorticity, indicating that the EHGT field is more appropriate to present the long-term variation in the SAH.
1 Introduction The South Asia High (SAH), sometimes referred to as the Tibetan High, is a planetary-scale anticyclonic circulation system in the upper troposphere and lower stratosphere (e.g., 200, 150 and 100 hPa) during the boreal summer, with its major body covering the entire eastern hemisphere from North Africa to the Date line in the subtropics (e.g., Mason and Anderson 1963; Krishnamurti and Bhalme Responsible Editor: A.-P. Dimri. * Xu Xue [email protected] 1
Department of Ecology, College of Life Science, Guizhou University, Guiyang 550025, Guizhou Province, China
2
Key Laboratory of Plant Resources Conservation and Germplasm Innovation in Mountainous Region (Ministry of Education), College of Life Sciences, Guizhou University, Guiyang 550025, Guizhou Province, China
3
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
1976; Tao and Chen 1987; Webster 2006). Several factors have been proposed to account for the formation and maintenance of the SAH, including the elevated heating of the Tibetan Plateau (e.g., Flohn 1960; Reiter and Gao 1982; Duan and Wu 2005; Boos and Kuang 20
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