Modulation of the Intraseasonal Variability of Early Summer Precipitation in Eastern China by the Quasi-Biennial Oscillation

Abstract. Using the reanalysis and multiple observations, the possible impact of the Madden-Julian Oscillation (MJO) on early summer rainfall in eastern China and its modulation by the Quasi-Biennial Oscillation (QBO) is examined. The composite results show that the suppressed (enhanced) convection anomalies for MJO phases 8-1 (4-5) more concentrated over maritime continent and western Pacific during EQBO (WQBO). As a consequence, more significant wet (dry) anomalies develop in South (eastern) China during MJO phases 8-1 (4-5) configured with easterly (westerly) QBO. The enhancement and expansion of the anomalous tropical convection band do not necessarily correspond to enhancement of the extratropical circulation response to MJO phases 8-1 (4-5) configured with westerly (easterly) QBO. The anomalous high (low) over the maritime continent and western Pacific associated with MJO phases 8-1 (4-5) is intensified (deepened) during easterly (westerly) QBO, leading to large southwesterly (northeasterly) anomalies in South China and coasts, carrying abundant (sparse) moisture. Two anomalous meridional circulation cells are observed for MJO phases 8-1 in the East Asia sector, with downwelling anomalies around 5–20° N, upwelling anomalies around 20–30° N, and another downwelling branch northward of 30° N, which are enhanced during easterly QBO. The anomalous meridional circulation cells are reversed for MJO phases 4-5, which are stronger during westerly QBO with the anomalous downwelling and dry anomalies covering eastern China. The combined impact of MJO phases 8-1 and easterly QBO on the early summer rainfall is noticeable in 1996 and 2020. The enormous rainfall amount appeared along the Yangtze River in 1996 and 2020 due to the extended period of the MJO phases 8-1 under the background of the easterly QBO.