How atmospheric instability influences models results of satellite observed upper tropospheric water vapor properties

The proper depiction of water vapor distribution in the upper troposphere and the related radiative properties is critical for the accuracy of climate and atmospheric circulation model predictions. In the present study, differences between satellite observations (Terra-MODIS) and atmospheric models´ simulations are examined. The models are: the National Center for Environmental Protection/Department Of Energy (NCEP-DOE) reanalysis-2 data and the Nonhydrostatic ICosahedral Atmospheric Model (NICAM). The models´ outputs (atmospheric temperature and humidity profiles) are used in this study to simulate the upper tropospheric brightness temperature (UTBT) and relative humidity (UTRH) at clear sky and low cloud areas. The results obtained show the contribution of atmospheric instability due to heat movements of the lower troposphere clear sky, cloud convection and low cloud radiative properties in the discrepancies between model and observation results. These differences tend to increase with the increase of the proportion of unstable pixels in the clear sky areas. Heat movements from cloud convection and low clouds examined through the convective clouds´ distribution and the cloud effective emissivity respectively, show that cloud convection mostly affects the NICAM model results (existence of a positive correlation between the latter model error and the amount of convective clouds) and, discrepancies are stronger in broken clouds than continuous clouds.