Upper- and Lower-tropospheric Circulation Anomalies Associated with Interannual Variation of Pakistan Rainfall during Su
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• Original Paper •
Upper- and Lower-tropospheric Circulation Anomalies Associated with Interannual Variation of Pakistan Rainfall during Summer Riyu LU1,5, Saadia HINA1,3,5, and Xiaowei HONG*2,4 1LASG, 2Key
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
Laboratory of Meteorological Disaster (KLME), Ministry of Education & Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science and Technology, Nanjing 210044, China
3Department
of Environmental Sciences and Engineering, Government College University, Faisalabad 38000, Pakistan 4Climate
Change Research Center (CCRC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
5College
of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing 100049, China (Received 6 May 2020; revised 16 July 2020; accepted 29 July 2020) ABSTRACT
This study investigated the large-scale circulation anomalies, in both the upper and lower troposphere, associated with the interannual variation of rainfall in Pakistan during summer, using the station observation data in this country and circulation data of the NCEP−NCAR reanalysis from 1981 to 2017. Results showed that the upper- and lower-tropospheric circulation anomalies associated with monthly rainfall variability exhibit similar features from June to August, so analyses were performed on June−August circulation and Pakistan rainfall data. The analyzed results indicated that summer rainfall in Pakistan is enhanced when there is an anticyclonic anomaly to the northwest of Pakistan in the upper troposphere and easterly anomalies along the southern foothills of the Himalayas in the lower troposphere, and vice versa. These upper- and lower-tropospheric circulation anomalies were found to be related, but show unique features. The upper-tropospheric anticyclonic anomaly is closely related to the Silk Road Pattern along the Asian westerly jet, while the lower-tropospheric easterly anomalies are related to the cyclonic anomaly to the south of Pakistan, i.e., intensified South Asian monsoon trough. The results presented here suggest that the interannual variability of summer rainfall in Pakistan is a combined result of upper- and lower-tropospheric circulation anomalies, and of extratropical and tropical circulation anomalies. Key words: rainfall, Pakistan, interannual variability, Silk Road Pattern, monsoon trough Citation: Lu, R. Y., S. Hina, and X. W. Hong, 2020: Upper- and lower-tropospheric circulation anomalies associated with interannual variation of Pakistan rainfall during summer. Adv. Atmos. Sci., 37(11), 1179−1190, https://doi.org/10.1007/ s00376-020-0137-0. Article Highlights:
• This paper identifies coupling processes related to Pakistan summer rainfall. • The coupling process includes an upper-level anticyclonic anomaly to the northwest of Pakistan and lower-level easterly anomalies in situ.
• This coupling process is similar between June
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