On Identifying the role of Sun and the El Nino Southern Oscillation on Indian Summer Monsoon Rainfall

Abstract

A solar influence on Indian Summer Monsoon (ISM) rainfall, identified in previous studies using the method of solar peak year compositing, may not be robust and can be influenced by other factors such as the El Nino Southern Oscillation (ENSO) and trends. Regression analysis, which takes into account variations across the whole solar cycle rather than just the minimum /maximum solar years, fails to detect any direct solar influence on the ISM during June–August. Regression suggests that the spatial pattern of ENSO, as imprinted in the sea level pressure in the Indian Ocean region, covering parts of Australia, has changed during the second half of last century. Thus ENSO impacts via variations in the local Hadley circulation may have played a role in modulating the ISM during that period. Finally, we discuss a possible indirect connection between the solar cycle and monsoon rainfall, which are different since the 1950s.