Evaluation of the Global and Regional Radiation Budgets of the NCEP CFS Reanalysis Relative to CERES EBAF Data

Reanalysis products are now accepted by many atmospheric scientists as the best available representation of the large-scale dynamical and thermodynamical state of the atmosphere. Reanalysis products are readily available from a number of weather and research centers and many researchers have used these products to investigate topics such as basic climatology, variability on diurnal to decadal scales, climate trends, and the global energy budget.

Reanalyses are based on data assimilation of profiles of atmospheric state variables measured by radiosondes and surface stations, as well as clear-sky radiances and retrieved quantities from satellites. However, cloud properties and radiative energy budgets are unconstrained by data assimilation in the current generation of reanalysis products. Clouds are produced by cloud parameterizations spun up from the assimilated dynamical fields and radiative fluxes are then computed from the assimilated thermodynamic profiles and model-generated cloud properties. Thus, the accuracy of cloud properties and radiative fluxes depends on model cloud parameterizations and radiative models, rather than on observations, and should be thoroughly evaluated before these variables are used in scientific studies.

Here we present the results of an evaluation of the radiative fluxes from the NOAA Climate Forecast System Reanalysis (CFS-R). The CFS-R shortwave and longwave fluxes at the surface and top of the atmosphere have been compared to values from the CERES Energy Balanced and Filled (EBAF) satellite data product on global and regional scales over monthly to decadal time periods. On average, the CFS-R global mean energy budget was found to agree well with the EBAF data; however, substantial differences were found on regional scales. These differences are related to cloud properties and surface reflectivity in the CFS-R. In addition, an unusual north-south pattern of disagreement was found in the reflected shortwave flux at the top of the atmosphere. Results of this evaluation will be presented and the observed differences explained.