HR: 11:05h
AN: A32B-04    [Abstracts]
TI: Upper Ocean Responses to Hurricane Frances in September 2004
AU: * Sanford, T B
EM: sanford@apl.washington.edu
AF: Applied Physics Laboratory, U. of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AU: Price, J F
EM: jprice@whoi.edu
AF: Applied Physics Laboratory, U. of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AU: Price, J F
EM: jprice@whoi.edu
AF: Woods Hole Oceanographic Institution, Physical Oceanography Department, Woods Hole, WA 02543, United States
AU: Webb, D C
EM: dwebb@webbresearch.com
AF: Webb Research Corporation, 82 Technology Park Drive, East Falmouth, MA 02536, United States
AU: Girton, J B
EM: girton@apl.washington.edu
AF: Applied Physics Laboratory, U. of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AB: Three new autonomous ocean velocity and density profilers were deployed ahead of Hurricane Frances as it passed north of Hispaniola in September 2004. These EM-APEX floats (velocity sensing versions of Webb Research Corp APEX floats) were launched from a C-130. The EM-APEX floats measured T, S and V over the upper 500 m starting about a day before the storm's arrival. One EM-APEX float was directly under the track of the storm's eye, another EM-APEX float went in about 55 km to the right of the track (where the surface winds are strongest) and the third float was about 110 km to the right. The EM-APEX floats profiled for 10 hours from the surface to 200 m then continued profiling between 30 and 200 m with excursions to 500 m every half inertial period. After 5 days, the EM-APEX floats surfaced and transmitted the accumulated processed observations, then the floats profiled to 500 m every half inertial period until recovered early in October aided by GPS and Iridium. The float array sampled in unprecedented detail the upper-ocean momentum, turbulence and salt and heat changes in response to the hurricane. Rapid acceleration of inertial currents in the surface mixing layer (SML) to over 1 m/s produced vertical mixing by shear instability at the SML base, as indicated by low Richardson numbers and SML deepening from about 40 m to 120 m under the strongest wind forcing. Surface cooling of about 2.2 C was primarily due to the SML deepening and entrainment of colder water, with a small contribution from surface heat flux. Intense inertial pumping was observed under the eye, with vertical excursions of 50 m or more. Comparison with a 3-D numerical model of the ocean response to Frances' winds simulates accurately SML deepening and surface cooling as well as significant differences in maximum currents and heat content changes. These differences highlight the sensitivity of the ocean's response to both the specification of the wind field and the parameterization of stress under high wind speeds. In particular, the momentum flux into the ocean supports a drag coefficient that does not increase with wind speed as proposed by recent GPS dropsonde and wind-wave tank studies.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4512 Currents
DE: 4544 Internal and inertial waves
DE: 4572 Upper ocean and mixed layer processes
DE: 4594 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly