As a key effort of the U.S. CLIVAR drought working group, several modeling groups have performed identical idealized experiments. The objectives are to address issues of model dependence on the response to SSTs and the role of soil moisture, and to investigate the physical mechanisms linking the SST changes to drought.

The modeling groups are the NASA/GMAO, the NOAA/NCEP/CPC, the LDEO/Columbia University, the NCAR CCSM, the NOAA/GFDL, and the COLA/University of Miami. The five AGCMs and one coupled AGCM participating in the project are the NASA NSIPP1, NCEP GFS, LDEO/NCAR CCM3, NCAR CAM3.5, GFDL AM2.1 and the NCAR CCSM3.0.

Three types of idealized experiments with the AGCMs are performed:

• Force the AGCM with leading patterns of SST variability (empirical orthogonal functions or EOFs), consisting of a linear trend EOF, an ENSO-like Pacific SST EOF, an Atlantic SST EOF that resembles the Atlantic Multi-decadal Oscillation, and their various combinations, with a repeating seasonal cycle.

• Same as above but with soil moisture feedback turned off

• Force the AGCM with low-frequency and ENSO patterns in the Pacific, with a repeating seasonal cycle

Please see SST_experiments.pdf for more details of the design of the AGCM runs and how the leading SST patterns are obtained, and see the Note for the EOFs and PCs of the leading SST variability. The EOFs and PCs of the leading SST patterns can be downloaded at the GMAO ftp site ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/README/SST_forcing/.

We note that, depending on factors such as personnel efforts and computational limitations, the five modeling groups selectively perform the idealized experiments that best fit their interests, and may not perform all the idealized experiments.

The NASA/GSFC GMAO hosts the outputs of the idealized runs and information on the AMIP runs by the five AGCMs at the GMAO ftp site ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/