Effects of Clouds on Surface Shortwave Irradiance in China: Estimation by Surface Radiation Measurements and Satellite Data

Abstract

 Clouds affect shortwave irradiance and the energy budget at the Earth’s surface. We investigated the potential radiative forcing in China by applying simple linear regression analysis on pyranometer measurements and data from the International Satellite Cloud Climatology Project (ISCCP). The potential radiative forcing is a measure of sensitivity of the surface shortwave irradiance to atmospheric parameters (here, cloud amount and cloud optical thickness). The negative correlation between the potential radiative forcing of cloud amount and cloud optical thickness strengthens with an increase in the cloud optical thickness up to about 8, after which it weakens. In contrast, the correlation coefficient between the cloud optical thickness and its potential radiative forcing varies widely for a low optical thickness and converges to a small negative value with an increase in the optical thickness; this is particularly true for data from the South and East regions. The potential radiative forcings obtained by analyzing pyranometer observation data are consistent with those calculated from ISCCP data in the previous study.