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This study examines the parameterization of monsoon rainfall over the Southwest US and Northwest Mexico using WRF simulations and NAME IOP data. The results and implications are discussed.
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Stephen W. Bieda III, Christopher L. Castro Department of Atmospheric Sciences University of Arizona North American Monsoon Rainfall Parameterization over the Southwest United States and Northwest Mexico: WRF Simulations using NAME IOP Data
Outline • Background and Motivation • Methods • Results • Discussion and Conclusions
Background Source: NAME Science Plan 2004 Source: Douglas et al. (1993)
Data Assimilation • It is clearly understood that assimilating data, or a lack thereof, can drastically affect the result of where rain will fall according to the model. • The NAME Science Working group has presented this issue as one of extreme importance, to improve forecasts in the NAME Regions (NAME SWG, 2005).
Motivation for Research • Though this serves as a term project for this class, the greater collaborative effort is between the University of Arizona’s Dept of Atmospheric Sciences and stakeholders across Arizona. • Known forecasting issues exist between the global forecasting models (i.e. NAM, GFS and Toby’s presentation yesterday). • This work was inspired by the Leuthold WRF Modeling Group, which 2 years ago showed the added value of working with a high resolution model.
Datasets NAME data archives (2004 field campaign) • This is the primary dataset with data that is assimilated into the model. A retrospective analysis is performed to ascertain whether the data provided in MX at the time helped improve forecasting efficiency. • Boundary conditions were forced by using NCEP ETA model data available for the July 20 to 25, 2004 IOP involving an inverted trough and intense convection in the NAM (North American Monsoon) core region.
WRF Model Settings • Two grids, with initial resolution set at 32 km, decreasing to 12 km around the core NAM region. • Convection was simulated using the Kain-Fritsch scheme. It should be noted that no other convective schemes were tried during the initial simulation start up. • No other “knobs” were attempted, as this exercise was meant to assimilate NAME data and to run WRF off of it.
Definition of Inverted Trough • Cyclonic circulation moving in a general westward direction across the NAME Tier I region. These are features in the middle and upper-troposphere with maximum vorticity occurring above 500 mb, and are typically “cold core” in nature (i.e. 500mb temps below -6C). Source: NAME Science Operation Plan (2004)
Conceptual Model of IV’s Source: Bieda et al. (2008)
Satellite Water Vapor taken 1224z 7/21 and 7/22 2004
Discussion • Due to the short term evaluation of 1 case study, it is hard to draw any major concluding points. • The major precipitation event that occurred in the southern Tier I region was captured relatively well by the WRF model, however precipitation was overestimated. • The WRF model was able to capture the MCV from NM relatively well, as reflected in the precipitation.
Conclusions • This is very much a work in progress that has only begun. User error is highly probably, so these results could be subject to that error. • However, it is heartening to see that the hindcasts using the IOP data and NAM externally forced boundary conditions produced decent results. • The ensemble precipitation reduced the amount of precipitation that did occur in AZ on both days, as well as in Sonora. This has been and continues to be a pesky problem for forecasters that latch onto the GFS and NAM for their precipitation forecasting.
Acknowledgements • I would like to thank Andy for helping me figure out why the WRFV3 model would not compile on my or any other computer. It was a great cause of frustration. • I would also like to thank Mike Leuthold for our discussions on the WRF model, which helped at least get me started.
