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Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events
Authors:WU Xiandu  RAN Lingkun and CHU Yanli
Institution:Wenzhou Meteorology Bureau, Wenzhou 325000, Nanjing University of Information Science and Technology, Nanjing 210044,Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089
Abstract:A moist thermodynamic advection parameter, defined as an absolute value of the dot product of horizontal gradients of three-dimensional potential temperature advection and general potential temperature, is introduced to diagnose frontal heavy rainfall events in the north of China. It is shown that the parameter is closely related to observed 6-h accumulative surface rainfall and simulated cloud hydrometeors. Since the parameter is capable of describing the typical vertical structural characteristics of dynamic, thermodynamic and water vapor fields above a strong precipitation region near the front surface, it may serve as a physical tracker to detect precipitable weather systems near to a front. A tendency equation of the parameter was derived in Cartesian coordinates and calculated with the simulation output data of a heavy rainfall event. Results revealed that the advection of the parameter by the three-dimensional velocity vector, the covariance of potential temperature advection by local change of the velocity vector and general potential temperature, and the interaction between potential temperature advection and the source or sink of general potential temperature, accounted for local change in the parameter. This indicated that the parameter was determined by a combination of dynamic processes and cloud microphysical processes.
Keywords:moist thermodynamic advection parameter  potential temperature advection  general potential temperature  heavy rainfall event
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