The tropical and extratropical-origin summer meridional teleconnections over East Asia

摘要

The meridional teleconnection over East Asia (EA-MT) is one of the major features of East Asian summer monsoon (EASM), and it is also the important pathway for the impacts from both tropical and extratropical middle-high latitudes on the EASM. To reveal the temporal-spatial structure of summer EA-MT, multivariate EOF is applied to the latitude-pressure cross section of combined summer precipitation and zonal wind anomalies over East Asia, using GPCP precipitation and NCEP/NCAR reanalysis dataset during the period 1979-2016. Two leading modes of summer EA-MT are obtained and identified as the tropical and extratropical-origin EA-MT in terms of their specific characteristics and major sources, named EA-TMT and EA-XTMT, respectively. Both of them show strong interannual variabilities, and they demonstrate a quasi-barotropic structure of westerly wind anomalies that slightly tilts northward with height in the mid-high latitudes, and accordingly significant precipitation anomalies are constrained right underneath the anomalous zonal wind around the Yangtze River valley (YRV), which in turn helps to establish and maintain the summer EA-MT. The EA-TMT is triggered by anomalous convective activities in the western North Pacific and propagates northward in the mid-low troposphere, it has close relationship with the anomalies of East Asian summer westerly jet (EASWJ) intensity and the YRV precipitation, which is superior over the East Asia/Pacific and Pacific-Japan teleconnection patterns in representing the tropical-origin EA-MT. The EA-XTMT is however mainly initiated in the southeast of Kara Sea and propagating southeastward in the whole troposphere, it is dominated by the North Asian dipole mode and mainly related to the EASWJ position anomaly, favoring a South Flood North Drought pattern of precipitation anomalies over East China. Meanwhile, the EA-TMT is closely related to the summer SST anomalies in the tropical Pacific-Indian ocean and partly correlated with ENSO, whereas the EA-XTMT is possibly linked to the spring sea ice concentration anomalies in the western Arctic and Barents Sea. Furthermore, the joint contributions of EA-TMT and EA-XTMT are essential for the major variability of EASM, wherein the EA-TMT plays a primary role.