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MMM SEMINAR NCAR

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Investigation of the Summer Climate of North America: A Regional

Atmospheric Modeling Study

Christopher L. Castro

Colorado State University

Ft. Collins, CO

With an appropriate experimental design, regional climate models (RCMs) are a valuable tool to enhance understanding of processes on the mesoscale, which is important when considering summer climate in North America. The first part of this study briefly focuses on developing that experimental design for the Regional Atmospheric Modeling System  (RAMS) by model modifications and a series of sensitivity experiments. Then a long-term (1950-2002) RCM climatology of the contiguous U.S. and Mexico is constructed by dynamically downscaling the NCEP Reanalysis. The RCM simulations are evaluated for boreal summer. An additional series of RCM simulations downscales data from the NASA Seasonal to Interannual Prediction Project (NSIPP) GCM, for GCM simulations executed with idealized SST distributions of the dominant modes of Pacific SST.  The RCM summer climatology for North America is reasonable, in light of observations and comparison to previous RCM results. The North American monsoon system is well captured. Time-evolving teleconnections associated with Pacific SSTs accelerate or delay monsoon evolution, and these appear in both the NCEP Reanalysis and NSIPP GCM data. A SST regime shift mode is associated with an increase in tropical SST, but has no relation to significant height anomalies in the midlatitudes. The most significant response in RAMS-generated fields, with respect to Pacific SSTs, occurs in late June and July. At this time, there is an opposite relationship between precipitation in the Southwest U.S. and central U.S.  The SST regime shift mode is associated with a general increase in atmospheric moisture and rainfall, except in western Mexico. A brief review of the 2005 North American monsoon season is presented, relating the May Climate Prediction Center forecast and results of this research.

Thursday, 20 October 2005, 3:30 PM

Refreshments 3:15 PM

NCAR-Foothills Laboratory

3450 Mitchell Lane

Bldg 2 Auditorium (Rm1022)