Extended Abstract (48K)P6.15
Ensemble forecasts using perturbed physics in a multidimensional parameter space
Raymond W. Arritt, Iowa State University, Ames, IA; and C. J. Anderson and W. A. Gallus
We have performed short-range (24 hour) forecasts using the NCEP Eta model in which closure constants in the cumulus parameterization scheme are varied across a range of plausible values. Although some previous studies have constructed ensembles by using models with different cumulus parameterization schemes or different values of closure constants, our study differs in that a multiple-dimension parameter space is constructed. This is done by varying two parameters within the Kain-Fritsch and Betts-Miller-Janjic schemes rather than only one parameter. Test cases will be shown in which two parameters are varied using four different values of each parameter, producing 4-by-4 matrices of simulations (i.e., 16-member ensembles). Results indicate that there are noticeable interactions between the two parameter specifications which would not be captured if only one parameter were varied at a time.
Ongoing research aims toward assessing value added by the ensembles in comparison to a reference forecast. Ensemble evaluations include relative operating characteristic as well as decomposition of mean square error into domain-mean and spatially-dependent components. Of special interest is the minimal ensemble size required to capture most of the value of the ensemble approach. Updated results will be presented in the conference.
Poster Session 6, Poster Session - Ensembles—with Coffee Break
Thursday, 2 August 2001, 2:30 PM-4:00 PM
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