Impact of solar variability on Indian summer monsoon through large scale circulations

Abstract

Via large-scale circulations, the role of solar variability on the Indian summer monsoon is investigated. Standardized anomaly is used to identify years of solar maxima and minima. Statistical analysis such as moving mean, empirical mode decomposition, and wavelet analysis are used to determine the plausible relationship between solar variability, large scale circulations such as El- Ni˜ no 3.4 SST anomaly, Dipole Mode Index (DMI), and Atlantic Multidecadal Oscillation (AMO), and Indian summer monsoon rainfall (ISMR). In addition, the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP-NCAR) reanalysis data collection is used to assess time-averaged composite anomalies of wind, latent heat, geopotential height during maximum/minimum solar activity years. The 31-years moving mean of DMI shows significant negative correlation ( 0.35) with sunspot number and with 31-years moving mean ISMR ( 0.28). Similarly, 31-years moving mean of AMO exhibits a substantial positive connection with ISMR (0.68) and Ni˜ no 3.4 SST shows significant negative correlation ( 0.62) with ISMR. Using intrusive mode function analyses it has noted that India receives rainfall for both phase of solar forcing but from wind studies at 850 hPa and 200 hPa, it is found that the phenomena for ISMR is different during solar maximum and minimum conditions. During solar maximum, a strong Low Level Jet is observed, and during solar minimum, a strong Tropical Easterly Jet is observed. Also, the area of influences of ISMR is different for solar maximum and solar minimum. The mean difference plot of seasonal rainfall shows that during solar maximum, north India receives reasonable amount of rainfall however during solar minimum, south India receives comparatively more rainfall than north India. A weakening of the local Hadley cell during solar minima is also observed.