An empirical model for estimating hourly solar radiation over the Indian seas during summer monsoon season

Abstract

123-131 Performance of the widely used Octa model [Quart. J. R. Met. Soc., 114 (1988) 165-182] for the estimation of hourly solar radiation over the Indian seas during summer monsoon season is evaluated. This model was found to overestimate radiation for all sky conditions, in particular for 7 and 8 octa cloud cover by 300 W.m-2. For overcast sky conditions, observed radiation was found to be independent of the altitude of the sun and dependent only on cloud thickness. The dominant cloud types observed during this period are thick cumulus and cumulonimbus with an average base height of 300-1000 m. With a view to improve hourly estimation of radiation for all cloud categories, a new set of regression equations was developed based on transmission of radiation in the atmosphere and the altitude of the sun. With the new model, estimation has considerably improved for all cloud amounts as indicated by the reduction in the standard error estimates, in particular for 7 and 8 octa cloud cover. Application of these two models to three independent data sets also suggests the suitability of the new model for the hourly estimation of radiation for monsoon cloud conditions over the Indian Seas. </smarttagtype