北非副热带高压与中亚夏季降水的关系

基于1979—2019年欧洲中期数值预报中心（ECMWF）的ERA-Interim逐月再分析数据和英国东安格利亚大学气候研究中心（CRU）的陆面逐月降水数据,分析夏季北非副热带高压（北非副高）与中亚夏季降水的关系。结果表明：北非副高的脊线指数和东伸脊点指数变化与中亚夏季降水联系紧密。在2个指数的单独变化和协同变化下,中亚夏季降水和大尺度环流异常分布存在很大不同。副高脊线主要导致中亚夏季降水南北反相变化,副高东伸脊点位置对中亚中南部降水存在重要影响。当副高位置偏东偏北时,里海和咸海上空受异常气旋控制,哈萨克斯坦大部分地区降水偏多,新疆受蒙古异常反气旋控制,降水偏少;当副高位置偏西偏南时,中亚地区主要受异常反气旋控制,其东北部存在异常气旋切变,对应中亚东北部降水偏多,其余区域降水偏少;当副高位置偏西偏北时,中亚上空受异常反气旋控制,大部分地区降水偏少;当副高位置东偏南时,中亚上空受异常气旋控制,热带印度洋水汽通过两步输送的方式,进入中亚上空,形成有利的动力和水汽条件,导致中亚大部分地区夏季降水偏多。

Relationships between North Africa subtropical high and summer precipitation over Central Asia

On the basis of the ERA-Interim monthly reanalysis data provided by the European Center for Medium-Range Weather Forecasts from 1979 to 2019 and Climatic Research Unit monthly precipitation data, the relationships between the North Africa subtropical high and the summer precipitation over Central Asia are analyzed. The results show that the variations of the ridge line index and eastern extension ridge index of the North Africa subtropical high are closely related to those of the summer precipitation over Central Asia. The effects of single and concurrent variations of the North Africa subtropical high on summer precipitation and circulations over Central Asia are significantly different. The ridge line of the subtropical high mainly affects the precipitation anomalies in the south and north parts of Central Asia, whereas the eastern extension ridge of the subtropical high plays an important role in modulating summer precipitation in the central and southern regions of Central Asia. Furthermore, we analyze the anomalous distribution of summer precipitation and atmospheric circulations under the concurrent variations of two indices. When the subtropical high shifts southeastward, there is an anomalous cyclone over the Caspian Sea and Aral Sea, corresponding to more summer precipitation over most areas of Kazakhstan. Meanwhile, Xinjiang is controlled by an anomalous anticyclone over the Mongolian Plateau, corresponding to less summer precipitation. When the subtropical high shifts southwestward, Central Asia is mainly controlled by an anomalous anticyclone, but there is an anomalous cyclonic shear in its northeast parts. Thus, more rainfall occurs in the northeast of Central Asia and less precipitation in other regions. When the subtropical high shifts northwestward, Central Asia is controlled by an anomalous anticyclone, corresponding to less summer precipitation. When the subtropical high shifts southeastward, Central Asia is controlled by an anomalous cyclone, and tropical Indian Ocean water vapor can enter Central Asia via two-step transportation, forming favorable dynamic and water vapor conditions; thus, Central Asia receives more summer precipitation.