Mesoscale surface analyses of the ERICA IOP-2 cyclone

Abstract

The mesoscale structure of an explosively deepening open-ocean cyclone, the Intensive Observation Period (IOP) 2 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) which occurred 13-14 December 1988, was studied. Aircraft, buoy and ship observations were plotted in 3 h blocks, and detailed hand-analyses of surface pressure and temperature, as well as frontal and cyclone structure, were prepared. The analyses were then converted to a 20 km grid using a Cressman analysis scheme, and the gridded fields passed to a Brown-Liu planetary boundary layer (PBL) model to calculate surface latent and sensible heat fluxes. The results of the mesoscale surface analysis showed that the regions east and northeast of the low featured less warm thermal advection than expected for a typical maritime cyclone and a low- level easterly flow that had a 5-10 C thermal disequilibrium between the sea surface and the overlying air. This caused substantial positive heat fluxes east of the low throughout the 12 h prior to and during rapid deepening. This pattern of surface interaction is substantially different from other cyclones and suggests that surface processes contributed significantly to the cyclogenesis.