Helene Brogniez

University of Chicago

Raymond T. Pierrehumbert

The goal of our project is to analyze the influence of a changing climate on both the distribution and the variability of the free tropospheric water vapor. The ultimate aim is to develop a better understanding of the operation of water vapor feedback. There are two parts to our proposed investigation.
The first analysis we will do aims to evaluate the performance of model water vapor dynamics in tropical and extratropical convective regions. This will be done using model-to-satellite comparisons against microwave satellite data. The specific satellite dataset we will use is AMSU-B. The advantage of using microwave data is that microwave emission is less affected by clouds than is infrared. The second analysis addresses the issue of whether changes in statistics of trajectories in a simulation of a changing climate have a strong effect on the probability distribution of relative humidity. The calculation follows a diagnostic trajectory-based approach along the lines carried out for the FOAM model in Pierrehumbert, Brogniez and Roca (2005, see preprint at http://geosci.uchicago.edu/~rtp1). The analysis uses as input the time-dependant wind and temperature fields from a control GCM run and a warm (eg. 4XCO2) run. Ideally, the data used should have at least 4xdaily time resolution.