Mesoscale Structures and Dynamics of Mid-Latitude Cyclones

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9632580 Hobbs Cyclones in middle latitudes affect large regions of the world. Consequently, improvements in understanding and forecasting of weather associated with middle-latitude cyclones has been one of the major goals of 20th century meteorology. Although very significant advances have been made in the basic understanding and ability to forecast extratropical cyclones on the large (synoptic) scale, progress in forecasting local precipitation and severe weather associated with these systems has been much slower. This is attributed to insufficient understanding of processes and phenomena on the convective scale (~0.1-10 km) and mesoscale (~10-1000 km). For the past twenty years or so, the cloud physics research group at the University of Washington has studied extratropical cyclones, with emphasis on the microphysics and mesoscale aspects of precipitation. These studies led to a classification and study of rainbands on the west coast of the United States, and studies of cyclones on the US east coast and in the central US. The latter two studies led to a proposal for a new conceptual model for cyclones that are generated in the lee of the Rocky Mountains, as well as to the identification of two large-scale rainbands that can produce severe weather in the central United States. The present research is an extension of these studies. Three main areas of research will be pursued. The first is to carry out further evaluations of the new conceptual model for cyclones in the central United States in order to improve its observational and theoretical foundation, and to increase its utility as a weather forecasting aid. The second task is to investigate the mechanisms responsible for the formation of narrow cold frontal rainbands, which are a ubiquitous feature of extratropical cyclones and can produce severe local weather. The formation of wide cold-frontal rainbands, another common feature of cyclones, will also be investigated. These studies will be carried out through detailed analyses of special data sets collected in three already completed field projects, and through numerical modeling studies of these cases using an advanced mesoscale model. ***