The Tropopause Inversion Layer in the GEOS-5 Data Assimilation: Sensitivity to the Observing System
Older global atmospheric data assimilation systems produce only a weak TIL in disagreement with observations. This has been attributed to excessive smoothing inherent in the data assimilation methodology. In this presentation we will demonstrate that, by contrast, the TIL is well represented in the Goddard Earth Observing System, version 5 (GEOS-5) analyses in terms of the season-dependent magnitude, vertical structure and extent, as permitted by the model resolution but there is a strong dependence of the analysis TIL on the observing system used. In particular, the insertion of conventional and hyperspectral radiance such as from the Atmospheric Infrared Sounder (AIRS) instrument data leads to a more realistic TIL. We will also briefly discuss the statistical distribution of Brunt–Väisälä buoyancy frequency above the tropopause as a measure of static stability and the sharpness of the TIL. Next, we will use the temperature tendencies computed by the GEOS-5 general circulation model in an attempt to separate dynamical and radiative contributions to the formation of the temperature inversion above the extratropical tropopause.