Observational Analysis of Tropical Cyclogenesis in the Western North Pacific. Part I: Structural Evolution of Cloud Clusters

Abstract

This paper is the first of a two-part series summarizing recent attempts to advance omit understanding of the physical processes associated with tropical cyclone formation in the western North Pacific. A combination of rawinsonde composite and individual case analyses are shown for both pre-cyclone tropical cloud clusters (genesis) and those-prominent cloud cluster that do not develop into tropical cyclones (nongenesis). This research is an extension of previous works at Colorado State University by McBride, Zehr, and Love. The first part of the study concerns the structural evolution of the genesis cloud clusters and nongenesis cloud clusters. Results show that nongenesis cloud clusters have about the same mean vertical motion and cumulus activity as the genesis cloud clusters. However, genesis cloud clusters are found to have much stronger middle-to low-level cyclonic circulation extending over a radius 2°?8° outward from the center. The buildup of this strong precyclogenesis circulation is associated with varying combinations of a stronger than normal monsoon trough and large-scale, low-level tradewind and/or monsoon wind surges.