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Role of salient potential‐vorticity elements in an event of frontal‐wave cyclogenesis

1999; Wiley; Volume: 125; Issue: 557 Linguagem: Inglês

10.1002/qj.49712555716

1477-870X

René Fehlmann, Huw C. Davies,

Meteorological Phenomena and Simulations

Abstract Extratropical cyclogenesis is usually accompanied by both an upper‐level trough and a surface front with its cloud‐diabatic accoutrements. In the present study these distinctive structures are interpreted as salient elements of the atmosphere's potential vorticity (PV) distribution, and their role examined for one particular event of frontal‐wave cyclogenesis. The strategy adopted is a form of diagnosis by PV dismemberment. It entails adopting a ‘successful’ forecast with a limited‐area model as a surrogate for the actual event, and then performing a sequence of simulations with modified initial conditions that correspond in each case to the removal of one (or more) of the salient PV elements. This approach provides an assessment of the relative significance of the individual elements, permits an insightful comparison of various extant theories of cyclogenesis, and pinpoints the particular PV elements influencing the event's predictability. It is shown that the replication of the simulated cyclone requires an adequate representation both of specific fine‐scale PV features at tropopause levels and of the diabatically maintained low‐level pre‐frontal PV band. Thus, a tenable theory of cyclogenesis that incorporates this not atypical event should both recognize and help clarify the dependence of cyclogenesis upon the relative locations, movement, scales and structures of the aforementioned salient PV elements.