Trends in surface radiation and cloud radiative effect over Switzerland in the past 15 years

Abstract

We analyzed 15 years (1996-2010) of high quality observations of surface down-welling short-wave and longwave radiation from four Swiss sites. Down-welling short-wave radiation at Locarno-Monti has significantly increased by 9 Wm−2 in the 1996-2010 period, whereas no significant trends at the 95% confidence level are observed at the other three stations. In addition, long-wave radiation has not significantly changed in the corresponding period. The cloud radiative effect was determined using radiative transfer calculations for the cloud-free short-wave radiation and an empirical scheme for the cloud-free long-wave radiation. Results indicate that the net cloud radiative effect has decreased by up to 7.5 Wm−2 which implies a reduction in fractional cloud cover over the four Swiss sites.