The Effects of Temperature Difference Between Cloud Base and Cloud Top on Surface Longwave Radiation Estimate Based on Calipso and Reanalysis Data

Abstract

The calculation of the SDLR is split into a clear-sky contribution calculated from bulk formula, and a cloud contribution depending on cloud fraction and cloud effective temperature (CET). This study used cloud base temperature (CBT) and cloud top temperature (CTT) as CET to estimate cloud contribution to SDLR, respectively. The retrieved SDLR are validated by the TIPEX-III surface budget network data. The validation results showed that accuracy of SDLR estimate was significantly improved when calculating cloud contribution using CBT compared with using CTT in Tibetan Plateau, especially when the surface elevation values for some sites are more than 4000 m, SDLR had higher accuracy with RMSE and BIAS of 27.46 W∙m-2 and -5.27 W∙m-2, respectively. However, when estimating cloud contribution with CBT, some SDLR inversion results had relatively lower accuracy. Reasons may be as follows: (1) when the surface elevation values for some sites are relatively lower, the CALIPSO product probably cannot detect the real cloud base; (2) and also, the multi-layer cloud may have not been considered.