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A Structure and Dynamics of Cold Fronts Observed in East Asia during Spring Part II: Dynamics of Strong Spring Cold Front

Li Zhenjun (Meteorological Center of Air Force, Beijing 100843) Zhao Sixiong (Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080)  
Based on the analysis of the cold front structure in Part I, the frontogenetical function was computed, conditional symmetric instability was discussed and then, the results of the diagnostic study were compared with Hoskins Bretherton (HB) model. The results are as follows: (1) Comparison of the various terms of frontogenetical function shows their orders are the same and the values of tilting term is larger than the others. In addition, the maxima of the total frontogeneticl function appears in the lower middle troposphere in the development stage of a front. (2) Conditional symmetrical instability has been evaluated. Several regions of CSI can be identified. It was noticed that the low level CSI is almost in same area that of the upward vertical motion (UVM) associated with the direct thermal circulation. Probably, the small moist symmetric instability could strengthen the intensity and decrease the scale of the UVM branch with respect to its vertical displacement. (3) Comparison between this analyses and model results of Hoskins and Bretherton reveals that the main features of the observed front agree qualitatively well with the model prediction. The major difference between the observed and model predicted fronts is that the subsidence in the cold air region is actually stronger than the mode prediction.
【Fund】: 国家自然科学基金
【CateGory Index】: P433
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