A Contrast Diagnostic Study of Two Cases of Explosive Northeastern Lows in Spring
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摘要: 该文选择了发展变化机制有一定差异的两例春季爆发性东北低压(分别是1983年4月25~26日气旋(简称A例)和1983年4月28~29日气旋(简称B例)),进行了对比诊断分析。结果表明:(1)非绝热加热和局地斜压不稳定对A例气旋发展来说是十分关键的因子,而空正IPV平流的显著增强及其与低层IPV分布中两个局地最大值的垂直耦合是B例气旋增强的一个重要原因;(2)两个风暴最大不同点在于非绝热加热效应在影响气旋增强的程度上有所不同。另外,B例事件中对流层中部产生的较强高空锋生可以在低压范围内导致深厚的上升运动并使高空锋向下游的正涡度平流得以加强,这对系统的发展是十分有利的。Abstract: The diagnostic study of two spring explosive northeast lows (Case A: 25~26 April, 1983; Case B: 28~29 April, 1983) is made. The IPV (Isentropic potential vorticity), frontogenesis and stability distributions have been calculated. The results show that: (1) The diabatic heating and local baroclinic instability are the crucial factors for case A; the rapid increases of the horizontal advection of potential vorticity and its vertical coupling with the high IPV in the low-level play an important role for the development of case B. (2) The greatest difference between the two storms is that the impacts of diabatic heating in degrees on cyclone intensity are different. And, another difference may be that cyclonic vorticity generated in the midtroposphere in connection with upper-level frontogenesis may contribute to the upward increase in cyclonic vorticity advection over the deepening storm center in case B.
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