The Role of Tibetan Plateau–Indian Ocean Thermal Contrast in the Significant Increasing Precipitation over the Southern Tibetan Plateau in May after the Mid-1990s

Abstract

This study investigates the impact of the interannual variation of Tibetan Plateau (TP)–Indian Ocean thermal contrast on southern TP precipitation in May and its changes in the mid-1990s. It is found that the southern TP precipitation is closely related to the TP–Indian Ocean thermal contrast, which could be represented by a thermal contrast index (TCI). The analysis reveals that the southern TP precipitation in May increases significantly after 1996. Meanwhile, the TCI also enhances notably. It is also found that compared with the period in 1979–96 (P1), the relationship between the southern TP precipitation and the TCI is more pronounced in 1997–2014 (P2). Further analysis shows that the meridional water vapor flux anomaly over the Arabian Sea (ABS_QV) acts as a linkage between the southern TP precipitation and the TCI. During P2, associated with the positive ABS_QV, positive water vapor flux anomalies emerge over the Arabian Sea and divide into two branches to the southwest of TP. One branch transports the moisture to the southern TP directly and forms a stronger southwesterly anomaly at the southwest edge of the TP than P1. The other branch stretches northward and imposes positive diabatic heating (Q1) anomalies over the Ural Mountains region (UMR_Q1). The results obtained by composite analysis and an anomaly atmospheric general circulation model both confirm that the UMR_Q1 anomalies can induce the wave activity propagating from the UMR_Q1 area to the TP and form the northerly anomaly over the TP, contributing to the convergence that favors the southern TP precipitation.