The Tropical Rainfall Measuring Mission (TRMM) was designed to measure and monitor precipitation throughout the tropics using a combination of a precipitation radar (PR) and a microwave imager (TMI), an instrument that uses microwave energy to measure characteristics of clouds and precipitation. Currently, rainfall analyses using TRMM and other satellite data extend into middle latitudes (up to 50� north and south). With the NASA Global Precipitation Measurement (GPM) mission planned for the near future, improving rainfall retrievals at higher latitudes will become even more important. Significant work is needed to fully understand the characteristics of precipitation at midlatitudes and determine how well we are able to measure these properties using data from TRMM and GPM. This proposal seeks to continue modeling work on precipitation from winter extratropical cyclones (low pressure systems associated with cold and warm fronts) performed under previous funding, but also emphasizes a new initiative to conduct a TRMM climatology of winter storms. The simulations will be conducted using either of two advanced numerical weather forecasting models: the PSU/NCAR mesoscale model (MM5) or the Weather Research and Forecasting (WRF) model nested to very high resolution (1-2 km grid scales). These are numerical weather forecast models that are well suited to studying precipitation processes. The specific objectives are 1) to continue analysis of an existing MM5 simulation of a winter frontal storm with an emphasis on comparing TRMM observations with corresponding model simulations and investigating the causes of significant differences between the two associated with the cloud physics; 2) to use the more advanced WRF model to conduct new simulations of winter storms observed during previous or upcoming field programs and to compare the numerical simulations to the field campaign data as well as to satellite remote sensors; 3) to examine the simulations, satellite observations, and field campaign data to study the mechanisms for precipitation formation and organization including potential effects of coastal mountains at landfall, the vertical structure of cloud and precipitation fields, and the relationship between these fields and the satellite observations and retrieved surface rainfall; and 4) to conduct a climatology of northern hemisphere winter precipitation at lower midlatitudes (24-36�N) to examine the distribution of precipitation characteristics and conduct more focused studies in specific regions of interest. The simulations can be used to improve the algorithms used to retrieve surface rainfall and atmospheric latent heating profiles and the research will investigate improvements to the parameterizations of cloud physics in the models. The research directly uses TRMM data in the study of individual cases as well as in a more climatological approach.
