Combination of ScaRaB‐2 and CERES with Meteosat‐5 to remove time sampling bias and improve radiation budget estimations in the INDOEX region

Abstract

Using data available over the INDOEX area, Meteosat‐5 visible and infrared data have been combined with ScaRaB/Resurs and CERES/TRMM broadband data for March 1999, and with CERES/TRMM and CERES/Terra data for March 2000. The study proceeds by collocation of the data sets, comparison of narrowband Meteosat radiances to broadband ScaRaB radiances, and conversion of radiances to fluxes. In the longwave (LW) domain, a multiple regression is found between ScaRaB and CERES fluxes, the two Meteosat infrared channels (infrared window and water vapor) and the viewing zenith angle. In the shortwave (SW) domain, narrowband‐to‐broadband (NB‐BB) and ERBE‐like radiance‐to‐flux conversions are applied. The RMS differences between the ScaRaB/CERES and Meteosat instantaneous flux retrievals are about 10 Wm−2 and 40 Wm−2 respectively in the LW and SW domains. A large part of these differences comes from the residual coregistration and narrow‐band‐to‐broadband conversion errors. On the contrary, the mean difference or bias between all data sets is very small, consistent at the 1% (LW) and 4% (SW) level. The LW and SW conversion equations have been used to convert Meteosat observations at each half hour into instantaneous broadband flux estimates consistent with the instantaneous CERES flux estimates for the same day. New monthly means are computed in this way: the changes are small in the LW but significant in the SW domain (regional means: ∼20 Wm−2, 20°S–20°N means: ∼4 Wm−2), especially for studies of long‐term changes.