The fluctuation of solar irradiance in Hong Kong

Abstract

Measurements of the total global solar irradiance on a horizontal surface in Hong Kong during the 10-yr period 1969-78 are analysed. Mean annual, monthly and daily totals and their frequency distributions are computed and examined. The seasonal and climatic effects on the fluctuation of solar irradiance in Hong Kong are discussed. The effect is particularly large during the spring months when the transition from cold to warm weather occurs. The diurnal variation of total global solar irradiance in Hong Kong is also examined and the measured hourly data are observed to be in good agreement with Liu and Jordan's procedure of estimation from daily totals. Results of regression analysis relating total solar irradiance with duration of bright sunshine hours based on data for Hong Kong are summarized. The yearly regression coefficients are found to be varying in an unsystematic manner. Estimation of the Hong Kong monthly average diffuse solar irradiance based on the correlation with the cloudiness index is also performed and the results are found to vary between 7.39 MJ m −2 d −1 in the summer and 4.44 MJ m −2 d −1 in the winter.