Evaluation of the distribution of subtropical free tropospheric humidity in AMIP‐2 simulations using METEOSAT water vapor channel data

Abstract

In the framework of the Atmospheric Model Intercomparison Project (AMIP) phase 2, we have established a diagnostic of the free tropospheric humidity (FTH) distribution using METEOSAT data over the 1984–1995 period for 14 climate models. The methodology of evaluation follows a two step “model‐to‐satellite” approach. First the raw METEOSAT “Water Vapor” radiances are simulated from the model profiles of temperature and humidity using the RTTOV‐7 radiative transfer model. Second, the radiances are converted into FTH using the same coefficients as in the satellite product offering a direct comparison. The analysis is focused on the dry subtropical areas observed by METEOSAT: the Eastern Mediterranean and the tropical South Atlantic Ocean. Most of the models reproduce the observed seasonal cycle both in terms of phasing and magnitude, despite an overall moist bias. A few models are in close agreement with the satellite data. The magnitude of the satellite estimated inter‐annual variability is also generally captured by models. Again, a small subset of models shows close agreement with the observations. This comparison suggests general improvements of the models with respect to the AMIP‐1 simulations.