Analysis of Meteorological Precursors to Ordinary and Explosive Cyclogenesis in the Western North Pacific

Abstract

Abstract Thirty-five cases of cyclogenesis that occurred during the cold seasons from 1975 to 1995 in the western North Pacific Ocean are studied to determine common and disparate dynamic and thermodynamic structures in both the ordinary and rapid developments. An analysis of 1000-hPa height and 1000–500-hPa thickness anomalies with respect to the 20-yr climatology reveals the following results. Though each sample of cyclogenesis is characterized by a favorable-appearing thickness trough–ridge structure, important differences are found. Both the upstream surface anticyclone and the downstream precedent cyclone are preferentially stronger at the beginning of the most rapid cyclogenesis in the strong sample. Because of the consequently stronger equatorward flow, the 1000–500-hPa thickness anomaly in the strong sample is colder by approximately 40 m (∼2°C) in the region of incipient cyclogenesis and eastward by 1500 km. A harmonic time series analysis of NCEP gridded fields partitions the geopotential height...