Evaluation of land-atmosphere interactions in models of the North American Monsoon

As part of the North American Monsoon Model Assessment Project 2, several regional and global numerical models simulated the 2004 North American summer monsoon season. Custom Model Output Location Time Series (MOLTS) were created at several key observational sites across Mexico and the southwest United States, allowing for unique comparability between observations and models. Output from the North American Regional Reanalysis (NARR) is also consulted. With temporal resolution of an hour on average, this dataset allows for analysis of key land-atmosphere interactions that govern the diurnal surface energy budget, and ultimately the vertical exchange of sensible heat in the monsoon. Surface-based evaluations of these 1-D processes in models are made, and implications of diurnal sensible heating differences on 850-500mb seasonal thickness are sought.

Beginning surprisingly with surface albedo, models exhibit substantial differences across the North American Monsoon region. Radiative feedbacks through afternoon cloud shading also vary. The magnitude of the Bowen Ratio, as well as its sensitivity to recent rain events (soil-moisture feedbacks), differs considerably as well. Consequently, net surface radiation and the continental heat source felt by large-scale dynamics vary considerably across models. The majority of models overestimate diurnal heating over the elevated Mexican plateau. Suggestive evidence for viewing these diurnal heating errors as a proxy for seasonal heating errors in models is given.