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Potential Vorticity Streamers as Precursors to Tropical Cyclone Genesis in the Western Pacific
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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The term tropical transition TT is used to describe the formation of a tropical cyclone from an extratropical precursor. The overarching goal of this thesis is to re-examine TT in the western North Pacific. This is accomplished via the synthesis of a subjective climatology of all tropical cyclones TCs from 2002-2008 and a case study analysis of ensemble prediction data for the particularly intriguing event of TS 16W in September of 2008. The climatological analysis indicated that TT events represented 14 of all TCs during the study period. The maximum frequency of TT events occurred in the late summer early fall. The resulting storm systems tended to form farther to the north than non-TT events and were found to be relatively weak and short- lived. The results of the case study analysis lend credence to the earlier finding that the genesis pathway of TS 16W exhibited a two-stage evolution. The first stage involved the forcing of near-continuous deep convection by a tropopause-level potential vorticity PV anomaly. The second stage involved the rearrangement of the upper-level PV structure via diabatic processes, resulting in a necessary reduction of vertical wind shear.
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