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The second phase of the North American Monsoon Experiment (NAME) Model Assessment Project (NAMAP2) was carried out to provide a coordinated set of simulations from global and regional models of the 2004 warm season across the North American monsoon domain. This project follows an earlier assessment, called NAMAP, that preceded the 2004 field season of the North American Monsoon Experiment. Six global and four regional models are all forced with prescribed, time-varying ocean surface temperatures. Metrics for model simulation of warm season precipitation processes developed in NAMAP are examined that pertain to the seasonal progression and diurnal cycle of precipitation, monsoon onset, surface turbulent fluxes, and simulation of the low-level jet circulation over the Gulf of California. Assessment of the metrics is shown to be limited by continuing uncertainties in spatially averaged observations, demonstrating that modeling and observational analysis capabilities need to be developed concurrently. Simulations of the core subregion (CORE) of monsoonal precipitation in global models have improved since NAMAP, despite the lack of a proper low-level jet circulation in these simulations. Some regional models run at higher resolution still exhibit the tendency observed in NAMAP to overestimate precipitation in the CORE subregion; this is shown to involve both convective and resolved components of the total precipitation. The variability of precipitation in the Arizona/New Mexico (AZNM) subregion is simulated much better by the regional models compared with the global models, illustrating the importance of transient circulation anomalies (prescribed as lateral boundary conditions) for simulating precipitation in the northern part of the monsoon domain. This suggests that seasonal predictability derivable from lower boundary conditions may be limited in the AZNM subregion. [ABSTRACT FROM AUTHOR]

This article highlights the North American Monsoon Experiment's (NAME) monsoon model assessment project. NAME will need to improve numerical simulations of the monsoon circulation and its large-scale effects to achieve its goals. The project's activities over the next few years are aimed at delivering models capable of forecasting the evolution of warm-season climate anomalies months to seasons in advance. NAME employs a tiered approach of monitoring, diagnostics and modeling in the heart of the monsoon region, on the regional scale, and on the continental scale, defined as Tiers I, II, and III, respectively. The project was designed to provide benchmark simulations of warm-season precipitation, and the physical processes that control precipitation, in Tiers I and II.