Hobart

Seminar Abstract

Friday 10 October 2008, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Thomas B Sanford
SECNAV/ONR Chair in Oceanographic Sciences
Applied Physics Laboratory and School of Oceanography
University of Washington, USA

Highly Resolved Observations and Simulations of the Ocean Responses to Tropical Cyclones

Tropical cyclones are responsible for thousands of deaths, billions of dollars of property and business losses, and disruptions to millions of peoples’ lives. Even slight improvements in the forecasts of cyclone track and intensity can have profound societal impacts. Much information is lacking about the details of the oceanic response. Yet, it is recognized that the ocean provides the sensible and latent heat (i.e. enthalpy) fluxes that initiate the tropical cyclones and also fuel its intensification.

I present results from rapid profiles of ocean velocity and density during the passage of Frances in September 2004. Three autonomous profiling EM-APEX floats were deployed ahead of this Category 4 hurricane and observed ocean properties every half hour over the depth interval 30 to 200 m – one on the forecasted track of the eye, others at 55 km to the right of the hurricane’s track and 110 km to the right of the track.

Each float observed different responses to the local wind velocities and durations. Under the high winds at the 55-km site, sea surface temperature (SST) cooled
2.2°C, SML deepened 80 m, and surface gravity wave reached 12-m significant wave height. Based on the momentum changes observed in the upper ocean, the apparent drag coefficient increased as described by Large and Pond, then decreased for winds greater than 25 m s^–1, and levelled off at 1.3 x 10^–3 at wind speeds greater than 35 m s^–1. Sea surface cooled primarily from shear induced vertical mixing bringing deeper, cooler water into the surface zone, rather than from sensible and latent heat leaving the ocean. Numerical simulations of the 3-D, time dependent ocean responses are improved with the in situ observations and their interpretations, such as the revised drag coefficient and SML deepening.

Seminar Recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Bernadette Sloyan, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5152
Thomas Kunz, (Biological seminars) CSIRO Marine and Atmospheric Research
(03) 6232 5076
Natalie Dowling, (Fisheries Modelling) CSIRO Marine and Atmospheric Research
(03) 6232 5148
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 21/07/09