NCEP/NCAR reanalysis data and NOAA OLR, Sea Surfact Temperature Anomalies (SSTA) data were used here to analyze the anomalous features of summer monsoon circulations in 2017 with extremely strong autumn precipitation Huaxi over western China, and to explore the mechanisms.The results show that WPSH is stronger and more northwestward, SAH (South Asia High) is stronger and more northeastward, Southwest Monsoon and Southeast Monsoon are both stronger, converge to Huaxi and meet with dry air, and work together to form an extreme strong autumn rain.The SST in the western equatorial Pacific and the Middle East have the positive and negative anomalies contrasted sharply, resulting in a strong Walker circulation, which made the typhoon in the western equatorial Pacific and the South China Sea active and formed a strong heat source.The central ascending airflow forms a strong secondary circulation with the tropical subsidence airflow south of 10°S; Various factors jointly strengthen WPSH and the southeast monsoon and guide the western Pacific and South China Sea water vapor into Huaxi.The cold air of Qinghai-Tibetan Plateau was weak with strong sensible heat.The convective and condensation latent heat was strong over northeastern Qinghai-Tibetan Plateau and Huaxi.So that the heat source was obviously stronger with significantly higher upper middle level temperature.It is beneficial to SAH, WPSH.It is another important reason for extreme heavy rain over Huaxi.In this case, the anomalous variation of the equatorial Pacific SST occurred in the late summer, one month before WPSH’s changing from weaker to stronger and is particularly important for short-term climate prediction and extended forecast.
Yuanyuan BAO
,
Yong LI
,
Zhiming KANG
. Characteristics and Mechanism of Monsoon Circulation Anomalies in Extreme Autumn Rain Over West China in 2017[J]. Plateau Meteorology, 2020
, 39(3)
: 560
-569
.
DOI: 10.7522/j.issn.1000-0534.2019.00056.
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