Extended Abstract (2.0M)6A.4
Impact of a warm ocean eddy's circulation on hurricane-induced sea surface cooling with implications for hurricane intensity
Richard M. Yablonsky, University of Rhode Island, Narragansett, RI; and I. Ginis
In recent years, it has become well-established that the upper oceanic heat content (OHC) in advance of a hurricane is generally a better indicator of potential hurricane intensification and maintenance than the sea surface temperature (SST) is. The OHC is important because a hurricane's surface winds mix the upper ocean and entrain cooler water into the oceanic mixed layer from below, subsequently cooling the sea surface in the region providing heat energy to the storm. For a given initial SST, since higher OHC reduces the wind-induced sea surface cooling, and warm ocean eddies have higher OHC than their surroundings, the argument is typically made that conditions become more favorable for hurricane intensification when the storm's core encounters a warm ocean eddy.
When considering hurricane intensity, one often neglected aspect of warm ocean eddies is the preexisting anticyclonic circulation in the eddy that exists due to the geostrophic adjustment of the density and velocity fields. Depending on the translation speed of the hurricane and the location of the eddy relative to the storm track, this anticyclonic circulation may impact the location and magnitude of the hurricane-induced sea surface cooling. Using a version of the Princeton Ocean Model, axisymmetric hurricane wind stress (plus asymmetry to account for storm translation speed) is applied to an initial ocean condition in which the SST is homogeneous, but an ocean eddy is embedded in an otherwise horizontally-homogeneous subsurface temperature field. One significant result from these model simulations indicates that when a warm ocean eddy is located to the right of the storm track, the interaction of the preexisting eddy circulation with the hurricane-induced cold wake can cause increased sea surface cooling under the core of the storm relative to the case where no ocean eddy is present at all. Therefore, the presence of a warm ocean eddy in advance of a hurricane may in some cases create a less favorable condition for hurricane intensification.
Session 6A, Ocean-atmosphere interactions and influences on tropical and extratropical storms: Part 1
Tuesday, 13 January 2009, 1:30 PM-3:00 PM, Room 128A
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