Polarimetric Radar Operation in Support of North American Monsoon Experiment (NAME)

Colorado State University, Fort Collins CO

Investigators

Abstract

The North American Monsoon Experiment (NAME) is a multi faceted research effort that strives to improve predictability of warm season precipitation over North America. Currently, the prediction of warm season precipitation on short- to medium-range timescales in the region extending from southern Mexico into the United States is hampered by a lack of understanding of precipitating systems within the monsoon, and the inability to accurately parameterize these precipitating systems in numerical weather prediction models. Several key interrelated physical processes fundamental to understanding and predicting the monsoon system remain poorly quantified, including: the bulk structure of the monsoon; the structure, kinematics, morphology, and diurnal cycle of individual precipitating systems (including mesoscale convective systems) within the monsoon; and, the interaction of precipitating systems with the variable surface properties in the region over the Sierra Madre Occidental (SMO), the Gulf of California and the intervening coastal plain, as well as the influence of the oceanic forcing on nearby continental precipitation (and vice versa), land surface memory processes, surface fluxes, and evapotransporation. To study these processes in detail, a comprehensive NAME Enhanced Observing Period (EOP) is planned for the Summer of 2004. Central to the goals of the NAME EOP is the continuous operation of the a research polarimetric Doppler radar, which will complement ongoing, long term observations and coincident EOP observations such as enhanced radiosonde, pibal, and profiler networks. Specific NAME EOP objectives key to the campaign that will be addressed under this research include: o documentation of the horizontal distribution of rainfall amount and intensity partitioned by convective and stratiform components, as a function of storm type, location, and environmental forcing; o measurement of the diurnal cycle of rainfall, convective intensity, storm morphology, and microphysics that will be crucial in diagnosing the physical processes behind precipitation in the region and thus links to predictability in the region; o identification of 2-D airflow within precipitating features, as well as other boundary layer flows including breeze fronts, gulf surges, and their role in convective initiation; o hydrometeor identification allowing evaluation of microphysical parameterizations in cloud resolving models and convective parameterizations in numerical weather prediction models. The Doppler and polarimetric data from NAME will be carefully analyzed using several existing methods. The polarimetric data will be used to identify dominant precipitation particle types in the convection and surrounding stratiform precipitation. The intellectual merit of this research consists of exploring the physical and dynamical characteristics of tropical convection in the immediate vicinity of significant topography. New results on the nature of tropical precipitation are expected to be gained from NAME. The Doppler data will provide for broader impact on the overall science by acquiring data to validate numerical models of the monsoon precipitation, and in particular, improving the ability to model the moisture transport into the southwest U.S. that drives the late summer rainfall in those regions. Hence better forecasts of heavy monsoonal rainfall in the southwest U.S. are expected as an outcome of NAME.