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David J. Gochis, W. James Shuttleworth, and Zong-Liang Yang

Abstract

This paper documents the sensitivity of the modeled evolution of the North American monsoon system (NAMS) to convective parameterization in terms of thermodynamic and circulation characteristics, stability profiles, and precipitation. The convective parameterization schemes (CPSs) of Betts–Miller–Janjic, Kain–Fritsch, and Grell were tested using version 3.4 of the PSU–NCAR fifth-generation Mesoscale Model (MM5) running in a pseudoclimate mode. Model results for the initial phase of the 1999 NAM are compared with surface climate station observations and seven radiosonde sites in Mexico and the southwestern United States. The results show substantial differences in modeled precipitation, surface climate, and atmospheric stability occuring between the different model simulations, which are attributable to the representation of convection in the model. Moreover, large intersimulation differences in the low-level circulation fields are found. While none of the CPSs tested gave perfect simulation of observations everywhere in the model domain, the Kain–Fritsch scheme generally gave significantly superior estimates of surface and upper air verification error statistics.

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David J. Gochis, Alejandro Jimenez, Christopher J. Watts, Jaime Garatuza-Payan, and W. James Shuttleworth

Abstract

Analyses of rainfall characteristics and their linkage to physiographic features are made from the North American monsoon experiment (NAME) Event Rain Gauge Network (NERN) in northwest Mexico. The findings are based on the network configuration for the 2002 and 2003 warm seasons. Despite the relatively short record used, a clearer structure of core-region monsoon rainfall is beginning to emerge. In agreement with earlier, coarser-scale studies, the seasonal precipitation maximum overlies the western slope of the Sierra Madre Occidental but does not strictly parallel a particular elevation band. It is shown that the distance to the Gulf of California and, potentially, the configuration of the terrain profile may also play an important role in determining where the axis of maximum precipitation lies. The diurnal cycles of precipitation frequency and intensity are shown to have distinct relationships to terrain elevation that are qualitatively similar to those observed over the Front Range of the Rocky Mountains in the central-western United States. The relationship between precipitation and gulf surge events occurring during the summer of 2003 is also explored.

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