The concurrent effects of the South Asian monsoon and the plateau monsoon over the Tibetan Plateau on summer rainfall in the Tarim Basin of China

Abstract

Based on the observed rainfall data at 34 stations over the Tarim Basin (TB) and the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data during 1961–2012, the concurrent effects of the plateau monsoon (PM) over the Tibetan Plateau and the South Asian monsoon (SAM) on summer rainfall over the TB are investigated. Mid‐upper tropospheric temperature (MUTT) plays an important role in linking the PM and the SAM with summer rainfall over the TB. The concurrent influential mechanisms of the PM and the SAM on summer rainfall over the TB can be summarized as follows. The strengthened (weakened) PM and the weakened (strengthened) SAM cause mid‐upper tropospheric cooling (warming), which tends to result in the migration of the subtropical westerly jet further southward (northward). Then an anomalous southerly (northerly) flow prevails over the TB, and more (less) water vapour is transported into the TB by a two‐step process. All above contribute significantly to an increase (decrease) in the occurrence of summer rainfall over the TB. In addition, we also discuss the relative contribution of the PM and the SAM to summer rainfall over the TB. Partial correlations show that the PM and the SAM can both individually influence summer rainfall over the TB. The PM has a direct effect on summer rainfall over the TB, for its considerable relations not only with MUTT but also with atmospheric circulation. Whereas the SAM has an indirect effect for its only influence on MUTT, which then give rise to an anomalous circulation related to summer rainfall over the TB.