Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events |
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Authors: | WU Xiandu RAN Lingkun and CHU Yanli |
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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 |
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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. |
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Keywords: | moist thermodynamic advection parameter potential temperature advection general potential temperature heavy rainfall event |
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