摘要
A crucial issue in evolution of severe storm, such as typhoon and even singlesupercell, is to diagnose and predict the sudden intensifying in storm. This paper describes anattempt to investigate the influence and effect of ambient moisture in the development of storm. Itwas mainly through a dynamic way to detect the helical enhancement by ambient moisture. It was foundthat the correlation between the ambient moistness and the intensity of rotating convective cellscan be well analyzed by helicity dynamics. The correlation between environmental streamwisevorticity (i. e. helicity) and vertical velocity (storm updraft or downdraft) is a powerfulindicator to catch favorable or unfavorable conditions for storm evolution. For this purpose, athree-dimensional non-hydrostatic storm-scale model, Advanced Regional Prediction System CARPS) wasemployed in order to numerically simulate a well-documented case of Del City supercell storm indifferent kinds of environmental moistness. Moreover, such different kinds of ambient moistenvironment and the resultant different morphologies and evolutions in the storm clearlydemonstrated that the abundant moistness in the environment that the storm embedded significantlystrengthens tbe storm intensity. In fact, the storm is embedded in much moist environment andtherefore larger instability propagates faster than the one in the drier air. It further producesstronger low-level mesocyclone with a much longer lifetime. The stronger convection and twist in theupdraft indicates that helical enhancement effect by moisture lead to stronger tornadic activity insevere storm.
A crucial issue in evolution of severe storm, such as typhoon and even singlesupercell, is to diagnose and predict the sudden intensifying in storm. This paper describes anattempt to investigate the influence and effect of ambient moisture in the development of storm. Itwas mainly through a dynamic way to detect the helical enhancement by ambient moisture. It was foundthat the correlation between the ambient moistness and the intensity of rotating convective cellscan be well analyzed by helicity dynamics. The correlation between environmental streamwisevorticity (i. e. helicity) and vertical velocity (storm updraft or downdraft) is a powerfulindicator to catch favorable or unfavorable conditions for storm evolution. For this purpose, athree-dimensional non-hydrostatic storm-scale model, Advanced Regional Prediction System CARPS) wasemployed in order to numerically simulate a well-documented case of Del City supercell storm indifferent kinds of environmental moistness. Moreover, such different kinds of ambient moistenvironment and the resultant different morphologies and evolutions in the storm clearlydemonstrated that the abundant moistness in the environment that the storm embedded significantlystrengthens tbe storm intensity. In fact, the storm is embedded in much moist environment andtherefore larger instability propagates faster than the one in the drier air. It further producesstronger low-level mesocyclone with a much longer lifetime. The stronger convection and twist in theupdraft indicates that helical enhancement effect by moisture lead to stronger tornadic activity insevere storm.
基金
ProjectsupportedbytheNationalNaturalScienceFoundationofChina(GrantNos:40175025,40333025and40028503)andtheStateKeyBasicProgram:(973)(GrantNo:2004CB418301).
