The increased rainfall in northwest India - coupled with the Northwestern Arabian Sea warming and modulated by the Silk Road Pattern after the late 1990s

Abstract

This study investigates changes in rainfall patterns over Northwest India (NWI) and the warming of the Northwestern Arabian Sea (NWAS) since 2000. These changes are attributed to the phase change of the Silk Road Pattern (SRP) in the late 1990s. The SRP positive phase affects geostrophic deformation over the Tibetan Plateau (TP) by inducing anomalous circulation patterns, such as anticyclone and cyclone at 200 hPa. This deformation along the westerly jets leads to jet streaks and thermally indirect ageostrophic circulation. Heating over the TP strengthens and shifts the South Asian High (SAH) westward. The interaction of positive temperature advection and northward ageostrophic wind generates a southward component of ageostrophic wind, causing upper-level convergence, sinking air, and increased surface pressure in the southeast of the TP. The intensified TP results in strong easterly wind anomalies along the monsoon trough, disrupting the monsoon circulation. These anomalies, combined with a poleward moisture-laden Low-Level Jet (LLJ), contribute to the warming of the NWAS and increased rainfall over NWI. The NWAS has experienced significant summer warming over the past two decades. The poleward shift of the LLJ and SRP-induced circulation changes also impact ocean dynamics. Given the occurrence of severe floods in this region of the Indian subcontinent, these findings have broader implications for predicting and projecting monsoon variability and extremes.