Sensitivity of Longwave Fluxes to Clouds and Meteorology: Establishing Uncertainties for GEWEX SRB Longwave Release 4

The NASA Global Energy and Water Exchanges (GEWEX) Surface Radiation Budget (SRB) project produces longwave and shortwave radiative fluxes for the surface and top-of-atmosphere (TOA). Along with improvements in the algorithms, the primary inputs of cloud and meteorology data have been undergoing improvements in quality and spatial and temporal resolution. Many of these inputs are being developed in collaboration with other GEWEX projects to ensure consistency between GEWEX radiation and other GEWEX data products (i.e., ISCCP, SeaFlux, LandFlux, GPCP, etc.). As part of this effort, the ISCCP is in the process of recalibrating and reprocessing its cloud properties with significant changes. In addition to cloud properties, ISCCP is reprocessing an atmospheric temperature and humidity data set called nnHIRS.

In this presentation, we present a sensitivity analysis of surface and TOA longwave fluxes due to changes in meteorology (temperature and water vapor) and cloud properties. The Langley Research Center Fu-Liou radiative transfer code (Rose et al. 2006) is used to conduct these sensitivity analyses. The sensitivity for surface and top-of-atmosphere radiative fluxes to meteorological changes is analyzed through the use of various sources of inputs from observational analysis such as ISCCP nnHIRS, NVAP-M, RSS MLS (v7) and AIRS. These meteorological data are compared to reanalysis products such as, GEOS-4 (used for the current GEWEX LW Rel 3.1 data set), MERRA, and MERRA-2. Together, these data sets provide uncertainty bounds in terms of the resulting radiative fluxes. We also assess the issue of the clear-sky versus all-sky fluxes since observational data sets like nnHIRS and AIRS do not provide full atmospheric temperature and humidity profiles under cloudy conditions. The reprocessed ISCCP cloud and meteorological data sets are planned to be inputs for the next version of the GEWEX SRB data set.