Influence of sunspot activity and EL Niño southern oscillation on northeast monsoon rainfall in the coastal districts of Tamil Nadu

Abstract

The current study is focused on establishing the effects of global variables such as the Sunspot Number (SSN)and El Niño Southern Oscillation (ENSO) on the local parameter, North East Monsoon Rainfall (NEMR) in the coastal districts of Tamil Nadu (CDTN) India from 1901-2020.  In the rising region of the solar cycle, excess precipitation is observed within about two years from the year of minimum SSN.  The solar cycle and rainfall (RF) have a 1-4year phase delay (solar cycle leads) of solar maximum.  The periodicity and phase delay of SSN and precipitation have been identified using Fourier Transformation and cross-correlation, respectively.  During the solar maximum, the precipitation is observed to be less.  The obtained results elucidate the inverse relationship between solar maximum and NEMR as well as the invariance of NEMR during solar minimum.  El Niño/La Niña and the sunspots maximum/minimum number have a high likelihood of co-occurring.  The correlation map analyzes the composite of OLR and excess/deficit NEMR years across two consecutive El Niño/La Niña years. This analysis confirms that prolonged El Niño events lead to excess rainfall, while La Niña events result in rainfall deficit.The Morlet wavelet transformation(MWT) analysis has been used to examine the temporal connection between SSN, ENSO, and NEMR cyclicities.  The findings of this study may be useful in predicting future droughts and wet years based on sunspot activity and to the policymakers for better management of water resources.