Validation of CERES/SARB data product using ARM surface flux observations

The Clouds and the Earth's Radiant Energy System (CERES) project (Weilicki et al. 1996) is a series of broadband scanning radiometers measuring total (0.3-oo um), reflected (0.3-5.0 um), and window (8-12 um) energy. The instruments, on board the Tropical Rainfall Measurement Mission (TRMM) and Earth Observing System (EOS) Terra and Aqua satellites, measure radiation at the Top Of the Atmosphere (TOA). CERES also produces, in the Surface and Atmospheric Radiation Budget (SARB) sub-system, vertical flux profiles in the atmospheric column beneath CERES footprints. This new data product supplies a global view of Earth's heating rates at 5 pressure levels from the TOA to the surface.

Model flux profiles are validated at the top of atmosphere by CERES observations. At the surface, observations of broadband insolation are necessary. To this end the CERES/ARM Validation Experiment (http://www-cave.larc.nasa.gov/cave/) was begun to collect these observations during CERES instrument's life span. This effort began in 1998 and continues to collect (and make available on the web) shortwave (SW) and longwave (LW) surface fluxes at over 40 sites around the globe. With improved inputs for aerosols over land from MODIS, in the Terra/Aqua time frame, comparisons of ARM/SGP and ARM/TWP observations show significant improvement over TRMM (1998) results.

CERES footprints are collocated to within 10km and 30 minutes of surface observations for Jan through Dec 2001. The majority of continental sites show good mean agreement for SW downward and LW upward and downward fluxes. Overall mean biases in SW insolation are less than 6W/m2 (~1% instantaneous) for "all sky" and less than 3W/m2 (~0%) for clear sky. LW flux down at the surface results show a mean bias ~3W/m2 (~1%) for all sky and less than 7W/m2 (~2%) for clear sky. The largest insolation differences are found under overcast skies with a difference of ~14W/m2 (5%) in SW insolation. All sky SW variability (RMS) is ~84W/m2 but for clear sky this drops to ~27W/m2. The largest differences occur around island based surface sites with RMS's well over 100W/m2. This RMS is halved under the few available clear sky footprints around these island sites.