2006 PSL Seminars
Understanding the Tropical Biases in GCMs: Double-ITCZ, ENSO, MJO and Convectively Coupled Equatorial Waves
NOAA ESRL and CIRES Climate Diagnostics Center
The tropical mean climate and tropical variability, such as the El Nino/Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO), play a key role for weather predictions, climate predictions and climate projections. However, they are not well simulated by the state-of-the-art general circulation models (GCMs) used for predictions and projections, and the problems are generally referred to as the tropical biases. The most prominent tropical biases are the double-ITCZ problem, the ENSO problem, and the MJO problem. These tropical biases have been persisting in the last several generations of GCMs. The major difficulties for understanding and alleviating these biases are twofold:
Multiple-model intercomparison, when combined with in-depth feedback analysis and direct model physics evaluation, provide a good way to overcome these difficulties. It can help us to understand the physical reasons of the tropical biases, find systematic dependence of the biases on specific model characteristics, and transfer the success of some of the models to other more bias-challenged models. We will present the results of several recent studies including:
Figures: Annual mean SST (shading) and precipitation (contour) for observation and 22 IPCC AR4 CGCMs. Contour starts at 5 mm/day with an interval of 2 mm/day. Models with heat flux adjustment are denoted by (adj). (b) shows the names used in this paper for the different geographical regions.
2:00 PM (Refreshments at 1:50 pm)
PSL-South Conference Room (1D403)