Variability and trends in low cloud cover over India during 1961-2010

Abstract

Annual and seasonal variability and trends in low cloud cover over India were analyzed for the period 1961-2010. Taking all period into account, there is a general decrease in mean low cloud cover over most regions of India, but an increase in the Indo-Gangetic plains and northeast India. Long term mean low cloud cover over India has inter-annual variations with highest cloud cover (39.4%) in monsoon and lowest cloud cover (10.5%) in winter season. The annual mean low cloud cover shows significant decreasing trend of -0.45% per decade, mainly contributed by monsoon where declining rate is -1.22% per decade. Out of the total numbers of stations showing decreasing trends, 65%, 47%, 53%, 71% and 37% of the stations show significant decrease in low cloud cover for annual, winter, summer, monsoon and post monsoon respectively, with large trend magnitudes occurring in central India. Spatially, the seasonal patterns of trends in low cloud cover confirm the annual patterns in most cases. Data analyses show that low cloud cover is having a strong negative correlation with maximum temperature and diurnal temperature range and a strong positive correlation with numbers of rainy days during the period of study.