Interdecadal variation of ENSO teleconnections to surface air temperature over central India during summer monsoon onset

This study investigates the interdecadal variations in the relationship between El Ni & ntilde;o-Southern Oscillation (ENSO) and surface air temperature (SAT) over central India in June. During post-El Ni & ntilde;o summers, north Indian Ocean (NIO) warming delays the onset of Indian summer monsoon (ISM), resulting in central India warming in June. However, this relationship weakened during 1960-1985 and subsequently recovered during 1986-2010 due to enhancements in the NIO warming response to El Ni & ntilde;o. In the latter epoch, south Indian Ocean warming during post-El Ni & ntilde;o spring (MAM) was significantly more pronounced than in the earlier epoch. This anomalous ocean warming triggers deep local convection and low-level convergence, accompanied by northeasterly wind anomalies in NIO. Concurrently, it generates tropospheric Kelvin waves that suppress convection over the tropical northwest Pacific (NWP) region, leading to an anomalous anticyclonic circulation (AAC) at low levels. The easterly wind anomalies on the south flank of the NWP AAC extend westerly to the NIO region, combined with the northeasterly wind anomalies, contributing to NIO warming in the subsequent June. This NIO warming leads to increased SAT over central India by delaying the ISM onset. During 1960-1985, these ocean-atmosphere coupled processes were considerably weaker, resulting in less NIO warming, a less delayed ISM onset, and reduced warming over the central India in June. Further analysis indicates that these decadal enhancements are attributed to the intensified thermocline feedback over the tropical south Indian Ocean and increased variance of ENSO itself, particularly in spring, with a regime shift around the mid-1980s.