The Rapid Growth and Decay of an Extratropical Cyclone over the Central Pacific Ocean

Abstract

The life cycle of a central Pacific cyclone, characterized by a 48-h interval of rapid fluctuation in its intensity, is examined. The cyclone of interest underwent a period of explosive cyclogenesis from 1200 UTC 4 November to 1200 UTC 5 November 1986, followed 12 h later by a period of unusually rapid decay. Output from a numerical simulation of this event, run using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5), is used to perform a piecewise potential vorticity (PV) inversion in order to diagnose the life cycle of this unusual cyclone. The analysis reveals that the presence of lower-tropospheric frontogenetic forcing in an environment characterized by reduced static stability (as measured by high values of the K index) produced a burst of heavy precipitation during the development stage of the cyclone's life cycle. The associated latent heat release produced a substantial diabatic PV anomaly in the middle troposphere that was, in turn, responsible for the majority of the lower-tropospheric height falls associated with the explosive cyclogenesis. Subsequent height rises during the rapid cyclolysis stage resulted from the northward migration of the surface cyclone into a perturbation geopotential ridge associated with a negative tropopause-level PV anomaly. This feature developed rapidly in response to the southeastward migration of a preexisting, upstream negative PV anomaly and the production of a second negative tropopause-level PV anomaly to the north of the surface cyclone. This latter feature was a diabatic consequence of the latent heat release that fueled the explosive development. Thus, the very latent heat release that assisted in the rapid development of the cyclone also played an important role in its subsequent decay. It is suggested that such a life cycle may represent an example of a “self- destroying” system.