26th Conference on Hurricanes and Tropical Meteorology


Surface fluxes and upper ocean budgets during 2002 Hurricanes Isidore and Lili

S. Daniel Jacob, Univ. of Maryland Baltimore County and NASA/GSFC, Greenbelt, MD; and L. K. Shay, G. R. Halliwell, C. J. Koblinsky, and M. D. Powell

The mutual hurricane-ocean response represents one of the most extreme air-sea interaction events. As the underlying boundary of hurricanes, the upper ocean plays a crucial role in the formation and maintenance of these storms. In particular, pre-existing oceanic mesoscale features such as energetic western boundary currents and warm core eddies have been shown to provide an important heat source for rapid intensification of hurricanes. In addition, strong currents associated with these features modulate the three dimensional mixed layer heat budget affecting sensible and latent heat fluxes to the atmosphere through horizontal advection. The objective of this paper is to understand the relative importance of key physical mechanisms within the context of predicting upper ocean heat content.

Using the Hybrid Coordinate Ocean Model (HYCOM), the upper ocean response during two 2002 major hurricanes (Isidore and Lili) is investigated in the Gulf of Mexico and Caribbean Sea. While Hurricane Isidore intensified to a Category 3 storm over the high heat content waters of the Caribbean Sea, Lili intensified rapidly over the Loop Current region where there is larger current variability. In addition, high-resolution atmospheric and oceanic measurements were acquired during these storms as part of a NSF/NOAA sponsored research. Therefore, these storms are ideal cases for investigating and quantifying the upper ocean response and associated feedback effects to the atmosphere.

Realistic pre-storm initial conditions for HYCOM in this study are derived from the 0.08 degree North Atlantic HYCOM that routinely assimilates altimetric height anomalies and therefore has major currents and eddies located in approximately the correct locations. Surface wind fields derived using buoy and aircraft measurements are blended with the large scale atmospheric model fields to provide boundary layer forcing every 3 hours for the two storms. Simulated ocean response and resulting fluxes for realistic and quiescent initial conditions for the same forcing will delineate the effects of pre-storm ocean variability. HYCOM simulations will be conducted using the 5 embedded upper ocean mixing parameterizations to evaluate their performance by comparing simulated fields to observations. We intend to identify the best vertical mixing submodels through this validation, which will also involve tuning the submodels and the surface flux parameterizations in HYCOM.

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Session 16A, sea-air interaction: Hurricanes Isidore and Lili
Friday, 7 May 2004, 8:00 AM-9:45 AM, Le Jardin Room

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