Surface Shortwave Radiative Fluxes Derived from the U.S. Air Force Cloud Depiction Forecast System World-Wide Merged Cloud Analysis

Abstract

Abstract We present a global-scale evaluation of surface shortwave (SW↓) radiative fluxes as derived with cloud amount information from the U.S. Air Force (USAF) Cloud Depiction Forecast System (CDFS) II World-Wide Merged Cloud Analysis (WWMCA) and implemented in the framework of the NASA Land Information System (LIS). Evaluation of this product is done against ground observations, a satellite-based product from the Moderate Resolution Imaging Spectroradiometer (MODIS), and several reanalysis outputs. While the LIS/USAF product tends to overestimate the SW↓ fluxes when compared to ground observations and satellite estimates, its performance is comparable or better than the following reanalysis products: ERA5, CFSR, and MERRA-2. Results are presented using all available observations over the globe and independently for several regional domains of interest. When evaluated against ground observations over the globe, the bias in the LIS/USAF product at daily time scale was about 9.34 W m−2 and the RMS was 29.20 W m−2 while over the United States the bias was about 10.65 W m−2 and the RMS was 35.31 W m−2. The sample sizes used were not uniform over the different regions, and the quality of both ground truth and the outputs of the other products may vary regionally. It is important to note that the LIS/USAF is a near-real-time (NRT) product of interest for potential users and as such fills a need that is not met by most products. Due to latency issues, the level of observational inputs in the NRT product is less than in the reanalysis data. Significance Statement We evaluate a current scheme to produce surface radiative fluxes in the NASA Land Information System (LIS) framework as driven with cloud amount information from the U.S. Air Force (USAF) Cloud Depiction Forecast System (CDFS) II World-Wide Merged Cloud Analysis (WWMCA). The LIS/USAF product is provided at near–real time and as such, fills a need that is not met by most products. Information used for evaluation are ground observations, MODIS satellite-based estimates, and independent outputs from several reanalysis. Since the various LIS products are used by the hydrometeorology community, this manuscript should be of interest to the users of the LIS/USAF information on surface radiative fluxes.