The Life Cycle of an Extratropical Marine Cyclone. Part I: Frontal-Cyclone Evolution and Thermodynamic Air-Sea Interaction

The Experiment on Rapidly Intensifying Cyclones over the Atlantic was carried out over the western North Atlantic Ocean to provide temporally continuous comprehensive datasets from which to document the life cycle of extratropical marine cyclones. The most intense cyclogenetic event occurred on 4-5 January 1989 over the warm (>20°C) Gulf Stream current; the cyclone's central sea level pressure decreased by 60 mb in 24 h, from 996 to 936 mb. This study presents the synoptic-scale and mesoscale life cycle of this cyclone in two parts. Part I, presented here, describes the 24-h frontal-cyclone evolution through 6-h analyses of observations taken by specially deployed observing systems from air, land, and sea. The analyses of temperature, wind, and pressure about the incipient cyclone first illustrate the precursor signatures to cyclogenesis. The 850- and 500-mb temperature evolutions show a significant departure from the Norwegian frontal-cyclone model. In particular, the 850-mb analyses document 1)...