Subsidence and Upper-Tropospheric Drying along Trajectories in a General Circulation Model

Abstract

A trajectory analysis of the Community Climate Model version 3 (CCM3) moisture simulation is used to show that the model simulates upper-tropospheric moisture observations better than would be inferred from a traditional geographical comparison. The upper-tropospheric moisture simulation is compared to upper-tropospheric moisture derived from Geostationary Operational Environmental Satellite 6.7-?m observations for September 1992. Trajectories start in convective regions of the Tropics and are followed into nonconvective subsidence regions. Moisture and pressure along the trajectories are determined for both the model and observations. Humidity values as a function of subsidence agree much better between observations and model than do geographical grid box comparisons, because the model does not simulate details in the large-scale flow pattern precisely. The relative humidity decreases slightly more slowly with subsidence along trajectories in the CCM3 simulation than in observations.