Trends in Radiative Fluxes Over the Indian Region

Abstract

The amount of solar radiation reaching the Earth’s surface is a major component of the surface energy balance and drives a large number of diverse surface as well as atmospheric processes. Over India, aerosols and clouds are the two major controlling factors that affect the shortwave and long-wave radiative fluxes. The present chapter reviews all the major studies carried out in India with respect to long-term variations in solar radiative fluxes in a changing climate scenario. Ground measurements of global irradiance data over India from 1981 to 2006 suggested a significant decreasing trend of 0.89 W m−2 year−1 under all-sky conditions, called solar/global dimming. Further, the long-term analysis of nearly four decades data from 1971 to 2010 showed a decreasing trend of 0.6 W m−2 year−1 during the period 1971–2000 and 0.2 W m−2 year−1 during the period 2001–2010.The lower trend value in the latter part is due to the reversal trends observed at some stations after 2001. This is also consistent with the decreasing trend in total cloud cover at some stations and suggests brightening of solar radiation.