A tripole winter precipitation change pattern around the Tibetan Plateau in the late 1990s

Classical monsoon dynamics considers the winter/spring snow amount on the Tibetan Plateau(TP)as a major factor driving the East Asian summer monsoon(EASM)for its direct influence on the land-sea thermal contrast.Actually,the TP snow increased and decreased after the late 1970s and 1990s,respectively,accompanying the two major interdecadal changes in the EASM.Although studies have explored the possible mechanisms of the EASM interdecadal variations,and change in TP snow is considered as one of the major drivers,few studies have illustrated the underlying mechanisms of the interdecadal changes in the winter TP snow.This study reveals a tripole pattern of change,with decreased winter precipitation over the TP and an increase to its north and south after the late 1990s.Further analyses through numerical experiments demonstrate that the tropical Pacific SST changes in the late 1990s can robustly affect the winter TP precipitation through regulating the Walker and regional Hadley circulation.The cooling over the tropical central-eastern Pacific can enhance the Walker circulation cell over the Pacific and induce ascending motion anomalies over the Indo-Pacific region.These anomalies further drive descending motion anomalies over the TP and ascending motion anomalies to the north through regulating the regional Hadley circulation.Therefore,the positive-negative-positive winter precipitation anomalies around the TP are formed.This study improves the previously poor understanding of TP climate variation at interdecadal timescales.

在20世纪70年代和90年代末,伴随着东亚夏季风的两次主要年代际变化,高原积雪分别显著增加和减少.尽管很多学者研究了东亚夏季风年代际变化的可能机制,高原积雪变化也被认为是主要因素之一,但是关于高原冬季积雪本身发生年代际变化的潜在机制尚鲜有研究.本文揭示了20世纪90年代末高原及周边冬季降水的三极子变化特征:高原主体上空主要为降水减少,其南北两侧区域降水增加.数值试验结果表明,热带太平洋海温变化可以通过调节沃克环流和局地哈德莱环流,对上述三极子降水变化型态产生显著影响.