Unprecedented East Asian warming in spring 2018 linked to the North Atlantic tripole SST mode

An unusually warm East Asia in spring 2018, when exceptionally high surface air temperatures were recorded in large areas of Asia, such as northern China, southern China, and Japan, was investigated based on the ERA-Interim reanalysis. The East Asian warming anomalies were primarily attributed to a tripole mode of North Atlantic SST anomalies, which could have triggered anomalous Rossby wave trains over the North Atlantic and Eurasia through modulating the North Atlantic baroclinic instability. Atlantic-forced Rossby waves tend to propagate eastward and induce anomalously high pressure and anticyclonic activity over East Asia, leading to a northward displacement of the Pacific subtropical high. As a result, descending motion, reduced precipitation, and increased surface solar radiation due to less cloud cover appear over East Asia, accompanied by remarkably warm advection from the ocean to southern China, northern China, and Japan. The transportation of anomalously warm advection and the feedbacks between soil moisture and surface temperature were both favorable for the record-breaking warmth in East Asia during spring 2018. The seasonal ‘memory’ of the North Atlantic tripole SST mode from the previous winter to the following spring may provide useful implications for the seasonal prediction of East Asian weather and climate.