Tuesday, 11 January 2005
Modeled moisture fluxes in the North American Monsoon Experiment region warm season
The study involves the modeling of moisture and moisture fluxes during the warm season over North America in general, and the North American Monsoon Experiment (NAME) region in particular. We already focused on results from the general circulation models in the second version of the Atmospheric Model Intercomparison Project (AMIP-2), where we found generally adequate simulation of the monsoon circulation system, where precipitation and moisture convergence in general advance from southern latitudes in the spring, achieve a nothernmost level in midsummer, and retreat in late summer/early autumn. The strength of this progression varies significantly in the AMIP-2 models, with important dependence on the land-surface characteristics, among other attributes. Here we also turn to the regional models to examine similar attributes of the monsoonal circulation. These higher resolution models, which have contributed to the NAME Model Assessment Project (NAMAP) have simulated one warm season. We can examine more clearly the moisture transport vectors and moisture divergences in that season with the regional models. Moisture flux patterns change significantly during the months constituting the monsoon season. In one such model, for example, early in the season, there is a build-up phase, in middle summer the mature phase of the monsoon with a gyre that includes the Gulf of California area, and the decay of the monsoon occurs in the autumn. Despite the general agreement in the seasonal cycle, differences exist between these models as well. There appears to be different amplitudes of the vertically integrated moisture transport vectors as well as their direction, sometimes significantly.