Collaborative Research: Improvement of Microphysical Parameterization Through Observational Verification Experiment (IMPROVE)

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Improvements in quantitative precipitation forecasting (QPF) have been listed as one of the top priorities of the U.S. Weather Research Program. The need for accurate QPF is especially acute along the mountainous coastal zone of western North America, where heavy precipitation and flooding are among the most significant weather hazards. Even with steady improvements in operational model resolution, quantitative precipitation forecasting has been slow to improve. This fact suggests that, in addition to increased grid resolution, other components of mesoscale models must be improved. One clearly problematic area is the bulk parameterization of grid-resolved cloud microphysics and precipitation. Under this collaborative project, two researchers from the University of Washington will execute a field program, associated data analysis and numerical modeling work, to improve quantitative precipitation forecasting in mesoscale models. The project will undertake comprehensive observational verifications and improvements of model-parameterized cloud and precipitation microphysics. The Principal Investigators will carry out two observational campaigns in the Pacific Northwest: a frontal precipitation study over the northeast Pacific Ocean offshore of Washington state in the winter of 2000/2001, and an orographic precipitation study in the Cascade Mountains of central Oregon in the winter of 2001/2002.Current bulk cloud microphysical parameterizations are based on relatively few observational studies; few dedicated efforts have been made to comprehensively evaluate the underlying assumptions and predicted hydrometeor distributions of these schemes, and to use such tests to improve the parameterizations. The only way to perform such verification in a manner that yields definitive and unambiguous results is to observe all aspects of the simulated precipitation system, from three-dimensional temperature and wind distributions to microphysical parameters such as mixing ratios and particle size distributions. This requires concurrent use of in situ cloud and precipitation microphysical observations from a well-instrumented aircraft and remotely sensed (radar) observations of the three-dimensional wind field. Recently, advances in numerical modeling, airborne microphysical measurement, and radar technology have converged to make such a study highly opportune. Furthermore, with a unique combination of scientific expertise, field project experience, observational facilities, and computing power, as well as a geographic location that experiences a high frequency of frontal and orographic winter precipitation systems, the University of Washington is ideally positioned to carry out the proposed research.(i)