Southward Shift of Westerlies Intensifies the East Asian Early Summer Rainband Following El Niño

Abstract

AbstractAn intensification of East Asian rainfall usually occurs in summers following El Niño. We propose that this teleconnection is mediated via the westerlies impinging on the Tibetan Plateau, through El Niño's control on tropical tropospheric temperature. This is distinct from previous studies that attribute the El Niño's influence to changes in the western Pacific subtropical anticyclone. The warming in the eastern equatorial Pacific leads to uniform warming of the entire tropical troposphere, which sharpens the temperature gradient between the tropics and the subtropics and shifts the westerlies southward. The westerlies impinge over the Tibetan Plateau for longer and, through interaction with the topography, induce intense and persistent extratropical northerlies downstream of the plateau that in turn intensifies the East Asian rainband. The rainband has previously been shown to intensify in a similar manner in a warming climate, suggesting that the El Niño response provides an analog for future changes.