Comparison of Earth radiation annual cycles from CERES and model computations

The annual cycle of absorbed solar radiation ASR, outgoing longwave radiation OLR and net radiation was computed from an eight-year data set from the Clouds and Earth Radiant Energy System (CERES) scanning radiometers aboard the Terra spacecraft. In support of the Terra and Aqua spacecraft science applications, Goddard Space Flight Centre generates the GEOS-5 data set, which includes the radiation budget components based on measured atmospheric parameters. The annual cycles of these model results were computed. In order to compare the annual cycles from these two data sets, the principal components PCs of each data set were computed to express the time variations and the corresponding empirical orthogonal functions EOFs were computed to describe the geographic variations. Ocean has a long thermal response time compared to land, so ocean and land were separated for the analysis.

The root-mean-square values for the annual cycles of the ASR, OLR and net are extremely close for the two data sets. The first three PCs are likewise quite close, showing that the time responses and magnitudes over the globe are very similar. The agreement between the two sets of PCs is quantified by computing the matrix of inner products of the two data sets. The EOF maps are similar for most of the globe, but differ in a few places. The agreements of the EOF maps are likewise quantified. Additional analysis is required to determine the reasons for these anomalies.