Different impacts of the variations of western and eastern portions of the East Asian westerly jet stream on southern China rainfalls in Meiyu season

Abstract

Variations of East Asian westerly jet (EAJ) drastically affect the rainfall in southern China (SC) during Meiyu season. Previous studies conventionally focused on the entire EAJ's variations and their impacts. In this study, we find that the variations of EAJ eastern section (EAJE) and western section (EAJW) are mostly independent of each other. Moreover, the independent components of EAJE and EAJW's variations have different impacts on the rainfall in SC. Southward-displaced and intensified EAJE (SI-EAJE) and southward-displaced and weakened EAJW (SW-EAJW), the first two leading modes of EAJ variations, are associated with increased rainfall anomalies centred over central and southern parts of SC, respectively.Associated with the SI-EAJE (SW-EAJW), anomalous cold cyclone is centred around the Japan Sea (central China). The associated anomalous westerly wind and northward-decreasing (northwestward-decreasing) temperature centred over the central (southern) SC together induce midtropospheric warm advection and thus positive rainfall anomalies centred over the central (southern) SC. The anomalous circulations also cause moisture convergences roughly collocated with the anomalous warm advections over the SC, which intensifies the rainfall anomalies.Warm sea surface temperature anomalies in the equatorial central-eastern Pacific during boreal spring induce meridional teleconnection along the coastal East Asia in Meiyu season through suppressing the convective activities in the northwestern Pacific. The resultant SI-EAJE and associated anomalous circulations increase the rainfall over the central SC, and vice versa. Dipole of increased (decreased) spring snow anomalies on the eastern (western) Tibetan Plateau suppresses (intensifies) convective activities in Meiyu season. The resultant SW-EAJW and associated anomalous circulations increase the rainfall in the southern SC.