Cloud Impacts on Korea Shortwave Radiation Budget: Estimation from a Deterministic Model with Surface Measurements

摘要

We estimated the Korea Shortwave Radiation Budget (KSRB) providing new insights into the Korea climate system. Monthly averaged clear-sky, overcast-sky, and all-sky flux measurements with cloud amounts from 2000 to 2015 were used to assess the impacts of cloud on the KSRB. A deterministic model for shortwave radiation transfer was utilized with climatological data to compute the monthly mean of KSRB at the surface, in the atmosphere and at the top-of-atmosphere (TOA). For 10 Korean stations ranging from 33.5°N to 37.7°N, the daily mean of incoming solar flux at TOA is 345.2 Wm~(-2). 45.5% of that is transmitted to the surface, 25.0% is absorbed in the atmosphere and 29.5% is reflected directly back to space by the cloud, atmosphere and ground surface under all-sky conditions. Under clear- and overcast-sky conditions, 63.2% and 24.9% are transmitted to the surface, 17.8% and 37.1% are absorbed in the atmosphere, whereas 19.0% and 38.0% are reflected to space, respectively, showing a remarkably invariant value with respect to locations. Clouds in all- (or overcast-) sky atmosphere diminish surface solar irradiances (SSI) from 218.1 Wm~(-2) to 156.9 Wm~(-2) (or 85.8 Wm~(-2)) and enhance atmospheric absorptions (AA) from 61.5 Wm~(-2) to 86.3 Wm~(-2) (or 128.2 Wm~(-2)). Clouds also enhance the reflected irradiances (RI) at the TOA from 65.6 Wm~(-2) to 102.0 Wm~(-2) (or 131.2 Wm~(-2)) for all- (or overcast-) skies. As a result, the all- (or overcast-) sky shortwave (SW) cloud forcing (CF) is -61.2 Wm~(-2) (or -132.3 Wm~(-2)) at the surface, AA is 24.8 Wm~(-2) (or 66.7 Wm~(-2)) in the atmosphere and RI is 36.4 Wm~(-2) (or 65.6 Wm~(-2)) at the TOA, respectively. Consequently, it is found that the values for SW-CF at the surface is 1.7 times and 2.0 times greater than that at the TOA in the KSRB under all- and overcast-sky conditions, respectively. We have also compared the KSRB with the global shortwave radiation budget (GSRB) and discussed on the shortwave radiation budget.