As part of a Hurricane Planetary Boundary Layer Experiment, Airborne Expendable Current Profilers (AXCPs) were deployed during the passage of East Pacific Hurricane Norbert and Atlantic Hurricanes Josephine and Gloria on September 23,1984, October 11, 1984 and September 26, 1985, respectively. The experiment was a joint effort between federal government and private industry which resulted in the first detailed current profile measurements below a hurricane. A total of 92 AXCPs were deployed in these storms, of which 45 transmitted useable data to the NOAA WP-3D aircraft Most of the failures occurred in the highest wind and wave regions according to Sanford et al (ref 1) A total of seven satellite-tracked drifting buoys were also deployed in Hurricanes Josephine and Gloria The Josephine buoys (3) were the Polar Research Lab (PRL) type and were equipped with an anemometer, pressure sensor, and a thermistor chain with sensors at the 40-, 60-, 100- and 200-metre levels. Initial results from analysis of this data set are provided in Black et al. (ref 2). The Gloria buoys (4) were the Horizon Marine type and were instrumented only for position and sea surface temperature(S ST).
The objective of the experiment was to measure the SST decrease induced by these hurricanes together with the storm-generated surface and subsurface current field in order to specify the dynamical processes which are involved. It is hoped that improved parameterizations of the SST decreases and storm-induced currents can be derived from this data set. It has been shown (refs 3 and 4) that the asymmetric SST distributions induced by hurricanes hay contribute to their asymmetric structure and reduce air-sea sensible and latent heat fluxes.
The Norbert observations revealed a divergent cyclonic circulation within the mixed layer similar to that predicted by recent numerical model simulations. Maximum mean mixed layer currents of 1.2m.s−1 were observed. Below the thermocline, a weaker anticyclonic circulation was observed, which resulted in 180° phase shifts in current vectors across the thermocline in most quadrants of the hurricane. Local Richardson numbers were less than 0.2 in the right-rear quadrant of Norbert, where sea surface temperature decreases of 2°C were observed in a crescent-shaped pattern centered at a radius 1.5 times the radius of maximum winds It is uncertain whether these strong currents and large shears are a result of enhanced surface stresses due to fetch-limited seas, as recently proposed by several authors, or to a resonant interaction of the hurricane wind field with inertially rotating currents.
The Josephine and Gloria observations revealed a more complex eddy pattern-induced by the interaction of the storm with the ocean Subtropical Front Maximum inertial current amplitudes of 0 6 m s−1 were observed, superimposed on the eddy currents The Gloria buoy observations were not capable of resolving inertial motions, but did reveal strong, divergent surface currents in the right-rear quadrant, in agreement with the Norbert observations.
Large surface wave-induced currents were observed in the right quadrants of these storms. The largest values of nearly 2 ms−1 were observed in Gloria with a period of 12 s.