Comparison of the effects of using the ECMWF ERA-15 and the NASA/DAO GEOS-1 re-analyses on the diurnal cycle of surface longwave fluxes

A surface radiation flux climatology is being produced by the GEWEX Surface Radiation Budget project by assimilating observations of earth's clouds and surface and estimates of atmospheric temperature and humidity profiles from re-analysis projects. Here we assess the uncertainties to the resulting radiative fluxes from this process by comparing the re-analysis simulations, GOES-1 DAO and ERA-15. In addition, these data sets will be compared with observational information from TOVS Pathfinder and NASA Water Vapor Project (NVAP). Particular emphasis is placed upon the evaluation of the effect the uncertainties from the re-analysis data sets on the surface flux estimates, with special regard placed on the diurnal cycle.

The comparisons will be conducted by averaging/integrating the temperature and moisture profiles over 3 vertical layers, to be designated as high, middle and low layers. The lowest layer will be subdivided to look at the effects of boundary layer temperature and moisture, especially important to the longwave fluxes. The diurnal cycles present in the reanalyses will be compared against those from actual surface observations. This is an important aspect of the current analysis because resolving the diurnal cycle on a 3-hourly basis is an objective of the GEWEX/SRB project.