High temporal variability of surface solar irradiance due to cloud enhancement effect over the Western Ghat mountains in peninsular India

Abstract

Western Ghat (WG) mountains along the west coast of peninsular India play an important role in the distribution of monsoon rainfall on its windward and leeward sides. The study unravels the increase in cloudiness and also increase in the Cloud Enhancement of Solar irradiance (CES) during the dry and wet seasons in the windward (high altitude) and the leeward (low altitude) sides of WG. From May 2018 to May 2021, the global horizontal irradiance (GHI) reveals wide temporal and spatial variability with a high frequency of CES events, even exceeding the extraterrestrial value around the noontime during the wet season (May to October). The observed excess irradiance due to partial/transparent clouds compared to clear sky maxima is more than 400 W/m2 on the windward and 350 W/m2 on the leeward. With the increase in cloudy days, diffused irradiance also increased with greater values during CES events. CES induced positive shortwave cloud radiative forcing (CRF) varied up to +400 W/m2 (warming effect), while negative CRF varied up to −1000 W/m2 (cooling effect). During monsoon, the warming due to frequent CES events could locally offset a large cooling to some extent. Clouds resulting in huge irradiance variability in a day could also induce large fluctuations in renewable solar energy. Such short-term sporadic local events are averaged out in satellite data.