Role of the Greenland Sea ice anomaly in the late-spring drought over Northwest China

Drought across Northwest China in late spring has exerted a vital effect on the local climate and agricultural production, and has been alleviated during the past decades. This study explored the influence of the preceding Arctic sea ice on the May drought in Northwest China caused by the precipitation deficit. Further analysis indicated that when the Greenland Sea ice concentration is abnormally high during February to April, the dry conditions in Northwest China tend to be alleviated. The increase of sea ice in the Greenland Sea can excite a meridional circulation, which causes sea surface temperature (SST) anomalies in the North Atlantic via the sea–air interaction, manifested as significant warm SST anomalies over the south of Greenland and the subtropical North Atlantic, but negative SST anomalies over the west of the Azores. This abnormal SST pattern maintains to May and triggers a zonal wave train from the North Atlantic through Scandinavia and Central Asia to Northwest China, leading to abnormal cyclones in Northwest China. Consequently, Northwest China experiences a more humid climate than usual. 晚春西北地区干旱的发生对西北地区气候和农业生产等具有重要的影响, 但在近几十年西北干旱状况呈现出缓解的趋势.本文研究了前期北极海冰异常对5月西北地区 (降水短缺引起的) 干旱异常的影响.进一步研究表明, 二至四月格陵兰海海冰偏多时, 西北地区干旱有所缓解.偏多的格陵兰海海冰可激发出经向环流异常, 环流异常通过海–气相互作用在北大西洋产生海温异常, 主要表现为格陵兰岛以南和北大西洋副热带海温偏高,亚速尔群岛以西海温偏低.这种海温异常可持续到5月, 并引发从北大西洋经斯堪的纳维亚半岛和中亚至中国西北地区的纬向波列, 并在西北地区产生气旋环流异常, 从而导致该地区水汽辐合, 干旱状况有所缓解.