Chapter 11 - Teleconnections between tropical SST modes and Indian summer monsoon in observation and CMIP5 models

Abstract

The Indian summer monsoon (ISM) plays a crucial role in the well-being of billion Indians. This study discusses teleconnection between ISM with two dominant tropical sea surface temperature modes, namely, the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Results are analyzed for observation and CMIP5 simulations in both historical and future scenarios. ENSO and IOD exert an offsetting impact on ISM. Due to an overly strong control by ENSO, the majority of CMIP5 models simulate an unrealistic IOD and ISM rainfall correlation, that might contribute to major uncertainties in ISM simulations in both historical as well as in future projections. For ENSO, the further focus was on the East Pacific type or Canonical ENSO and the Central Pacific type or ENSO Modoki, and their regional teleconnection was explored. Regions of Central North East India suggest strong teleconnection in models that matches with observation, though for ENSO Modoki case that completely disappears in the future. In terms of mechanism, tropic and mid-latitude connection, the influence of regional Hadley circulation, and the role of the Sun were addressed. Finally, a hypothesized mechanism was proposed for disruption of ISM–ENSO teleconnection in the latter two decades of the last century.