Effects of clouds on surface radiation from ground-based observation and Monte-Carlo radiative transfer model

Interaction between cloud and solar radiation is very important in understanding earth’s radiation budget, but involves various complexities in real atmosphere. Generally, clouds attenuate the incoming solar radiation, but scattered clouds can increase UV radiation locally. This study presents the enhancements of observed UV radiation with respect to cloud amount and type. In this study, UV (286.5~365nm) irradiance observed by a Brewer spectrophotometer (MK-IC, NO. 148) installed at the rooftop of Science Hall at Yonsei University (37.33°N, 126.56°E), Seoul, Korea were used. Moreover, sky image which were taken at every 10 minute by a digital camera, Sky-view (PREDE) at the same place is used. Because the process between cloud and radiation involves three-dimensional feature, a Monte-Carlo radiative transfer model, I3RC(Cahalan et al.2005), were used to calculate radiation field considering three-dimensional clouds. As a result, the enhancement due to clouds momentarily occurred up to 85% of total UV irradiance in clear sky, especially in broken cumulus clouds.