The GPCI (GCSS/WGNE Pacific Cross-section Intercomparison), is a model intercomparison project that has collected output from as many as 23 different GCMs from several international groups active in climate research. The database of model results describes the atmospheric physics in the Eastern Pacific sector of the Hadley Cell. Systematic analysis of that data set, based on extensive comparisons between model parameters and different observations is being perfomed. This type of model evaluation aims at complementing the more traditional efforts in GCSS as the SCM/LES/CRM methodology does not allow for feedback to the large-scale dynamics. The main focus of the research is the representation of convection and clouds by global models in two remarkable areas of the global circulation: the subtropical region of stratocumulus and the deep convection belt near the Equator (as well as the transition between them). A step forward has been taken in GPCI relatively to other similar intercomparisons in regard to the use of high temporal resolution model results (every 3 hours for JJA 1998 and 2003) and observational data. This will be particularly important in trying to understand boundary layer mixing and convection, and particularly the transition from cloud-topped boundary layers (stratocumulus to cumulus) to deep convection in the low-latitude marine environment.

In this work we use information on relative humidity (RH) in the troposphere, derived from a new data set of recently available observations from the Atmospheric Infrared Sounder (AIRS, onboard NASA's Aqua satellite), to evaluate the simulations from a sub-set of the GPCI climate models. We attempt to better understand the variability (mean, temporal evolution, standard deviation, etc) of humidity in the troposphere comparing daily averaged output from the models to the satellite data (daily profiles of RH for the 13 locations along the GPCI cross-section obtained from Level 3 products) for the season JJA of 2003. To facilitate comparisons with AIRS observations, we take into account only those simulated profiles with total cloud cover less than 70%. The AIRS instrument (~2400 channels) suite is a nadir scanning sounder with combined infrared and microwave retrievals. Aqua is in a sun-synchronous polar orbit, with an equatorial crossing at ~1330 and ~0130 local time.

Finally, we take a glimpse at preliminary results of CloudSat and Calipso cloud occurence (derived from 2B-GEOPROF-LIDAR) data for the GPCI cross-section for the season JJA of 2006. We compare this to climate model simulations of cloud cover. CloudSat (RADAR measurements) and Calipso (LIDAR measurements) are (along with Aqua) members of the NASA's A-Train, a constellation of six satellites flying in formation in close proximity.