TROPICAL CYCLONE MOTION AND SURROUNDING FLOW RELATIONSHIPS - SEARCHING FOR BETA-GYRES IN OMEGA-DROPWINDSONDE DATASETS

In 1982, the National Oceanic and Atmospheric Administration's Hurrica ne Research Division began a series of experiments to collect Omega dr opwindsonde (ODW) observations within about 1000 km of the center of t ropical cyclones. By 1992, 16 ODW datasets had been collected in 10 At lantic basin hurricanes and tropical storms. Objective wind analyses f or each dataset, at 10 levels from 100 mb to the surface, have been pr oduced using a consistent set of analysis parameters. The objective an alyses, which resolve synoptic-scale features in the storm environment with an accuracy and confidence unattainable from routine operational analyses, have been used to examine relationships between a tropical cyclone's motion and its surrounding synoptic-scale flow. Tropical cyc lone motion is found to be consistent with barotropic steering of the vortex by the surrounding Bow within 3 degrees latitude (333 km) of th e cyclone center. At this radius, the surrounding deep-layer-mean flow explains over 90% of the variance in vortex motion. The analyses show vorticity asymmetries that strongly resemble the beta gyres common to barotropic models, although other synoptic features in the environmen t make isolation of these gyres from the wind fields difficult. A reas onably strong relationship is found between the motion of the vortex ( relative to its large scale surrounding flow) and the absolute vortici ty gradient of the vortex environment.