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The Department of Meteorology is involved in research on the North American (Mexican) Monsoon in Arizona and the U.S. Southwest.

The objectives of this project are:

• To achieve a better understanding of the evolution of the North American monsoon system and its variations.
• To achieve a better understanding of the response of warm season atmospheric circulation and precipitation patterns to slowly varying boundary conditions (e.g. sea surface temperatures—SSTs, soil moisture), using advanced computer models.
• To run atmospheric mesoscale models (MM5 and WRF) utilizing the parallel-processor supercomputer on the Prescott Campus.

Our work focused on developing simple conceptual models of the monsoon using mesoscale computer models simulations and validation from remote sensing imagery and other meteorological datasets, involving some of our meteorology students to participate in undergraduate research.The key problem of any mesoscale model is the calculation of the model physics. Different convective parameterization schemes (CPS) result in a different seasonal evolution of the North American Monsoon (NAM). Running mesoscale models over the whole NAM region presents convective parameterization challenges, because different CPS's have assumptions and parameter specifications that make them more appropriate in some regions than others.This is complicated over the NAM domain, which is of appreciable size and variable topography. In our future work this year we want to expand upon the sensitivity studies using WRF, which is the most physically complex and appears to generate convective precipitation more realistically in the north of the NAM region.In our simulations so far, MM5 correctly predicted the development of the deep, monsoon PBL, and consequently did a good job of predicting the convective available potential energy and downdraft convective potential energy. Our coarse grid includes the entire monsoon domain. The nest comprises Central and Northern Arizona centered around Prescott Campus.During the 72-h simulations, a four-dimensional data assimilation (FDDA) procedure was used to insert atmospheric data into the model through a Newtonian relaxation nudging procedure. Newtonian relaxation terms are added to the prognostic equations for wind, temperature and water vapor.Our research indicates that the onset time of relatively heavy summer rainfall in Arizona generally occurs several days after the sea surface temperature (SST) in the northern Gulf of California reaches or exceeds 29.5°C. Our simulations using mesoscale model confirm this result, showing a dramatic increase in boundary layer moisture, convective available potential energy (CAPE), and updraft velocities over the GC region when N.-GC SSTs increase from 29°C to 30°C.