Mesoscale vertical structure of an explosive oceanic cyclone.

Abstract

The mesoscale vertical structure of an explosively deepening oceanic cyclone on 19-20 January 1989 during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) was studied. Hand analyses of height, temperature, and dewpoint, and cross-sections of 6 and 6, were prepared using aircraft and sounding data through the warm-frontal region in order to document the vertical structure. The results showed that the initial disturbance formed under a region of strong upper-level confluence between a southern jet streak and an approaching upper-level short-wave from the northwest. Upper-level frontogenesis associated with the confluent flow was strong enough to produce tropopause folding and stratospheric extrusion as low as 700 mb about 750 km upstream from the surface low prior to rapid deepening. The mesoscale analyses during the initial occlusion phase showed the upper-level temperature and moisture patterns spiraling around the low center with strong warm air advection occurring under a pocket of cold air aloft, producing significant convective instability. The cross-sections of 6f throughout the rapid deepening period showed unstable conditions, which suggests that moist potential instability in the warm frontal region was a factor in the rapid development of this storm.