Sensitivity of atmospheric circulation models to upper tropospheric relative humidity derived from satellite observed radiances

Meso-scale atmospheric models outputs are valuable data for cloud and aerosols retrievals. In view of the launch the Global Change Observation Mission-Climate/Second generation Global Imager (GCOM-C/SGLI) satellite, atmospheric models products are tested against satellite observations data in order to evaluate the degree of reliability and the sensitivity of these models outputs to variations of atmospheric conditions. The analyses presented in this study are based on two models outputs: the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) and the National Center for Environmental Protection/Department Of Energy (NCEP/DOE) re-analysis-2 data. Terra/Moderate Resolution Imaging Spectrometer (Terra/MODIS) satellite sensor observations of water vapor radiances are used as the verification data set for the tests conducted. These tests are based on the comparison between upper tropospheric water vapor properties (clear sky and above-low clouds) observed by satellite and radiative transfer forward calculations (using models' predicted atmospheric profiles, the satellite sensor spectral response and geometrical characteristics) derived from NICAM and NCEP/DOE. The parameters measured are the upper tropospheric brightness temperature (UTBT) and relative humidity (UTRH). Discrepancies between simulated data and observations are analyzed in terms of atmospheric instability, cloud convection movements and, effective emissivity. The results obtained show that both NICAM and NCEP/DOE simulated UTBT and UTRH outputs have a relatively comparable distribution pattern. However, simulations performed with the NCEP/DOE outputs present generally fewer discrepancies with satellite observations. For the interpretation of these results, the stability index study shows that differences between models and observation data tend to be high in unstable atmospheres. This atmospheric instability can be attributed to cloud convection processes affecting areas adjacent to convective clouds. As the amount of convective clouds increases, the errors in the water vapour depiction by the models increase also. Analyses of heat movements studied through the variation of the cloud effective emissivity suggest that the discrepancies between the observations and the models increase with the decrease of the clouds' effective emissivity. Adjustments of some of the models parameters, notably the microphysical parameterization of the clouds resolving scheme, are suggested in order to improve the accuracy of the models' results.