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.

中文翻译：

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与巴基斯坦夏季降水年际变化相关的对流层上下环流异常

本研究利用巴基斯坦1981年至1981年间的台站观测资料和NCEP-NCAR再分析环流资料，研究了与巴基斯坦夏季降水年际变化相关的对流层上下大尺度环流异常。 2017. 结果表明，与月降雨变化相关的对流层上下环流异常在6-8月表现出相似的特征，因此对6-8月环流和巴基斯坦降雨数据进行了分析。分析结果表明，对流层上部巴基斯坦西北部有反气旋异常，对流层下部喜马拉雅山南麓有东风异常时，巴基斯坦夏季降水增强，反之亦然。这些对流层上层和下层环流异常被发现是相关的，但表现出独特的特征。对流层上层反气旋异常与亚洲西风急流的丝绸之路模式密切相关，而对流层下层东风异常与巴基斯坦南部的气旋异常，即加强的南亚季风槽有关。这里展示的结果表明，巴基斯坦夏季降雨的年际变化是对流层上层和下层环流异常以及温带和热带环流异常的综合结果。而对流层低层偏东异常与巴基斯坦南部的气旋异常有关，即南亚季风槽加强。这里展示的结果表明，巴基斯坦夏季降雨的年际变化是对流层上层和下层环流异常以及温带和热带环流异常的综合结果。而对流层低层偏东异常与巴基斯坦南部的气旋异常有关，即南亚季风槽加强。这里展示的结果表明，巴基斯坦夏季降雨的年际变化是对流层上层和下层环流异常以及温带和热带环流异常的综合结果。