The long-term variation in the South Asia High intensity measured by 150-hPa eddy geopotential height
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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.
We thank two anonymous reviewers for their constructive suggestions and comments, which helped to improve the paper. This study is jointly supported by the National Natural Science Foundation of China (Grant No. 41705069), the Science and Technology Project of Guizhou Province (Talents of Guizhou Science and Technology cooperation platform, 5788), and the Scientific Research Project of Introduced Talents of the Guizhou University (No. 2016(34)).
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Conflict of interest
The authors declare that they have no conflict of interests.
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