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

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.