Extended Abstract (104K)17A.2
Observational Analysis of Buoyancy in Eyewalls of Intense Hurricanes
Matthew D. Eastin, Colorado State University, Fort Collins, CO
Flight-level data from 14 intense hurricanes are used to statistically examine buoyancy in convective updraft cores at the lower and middle levels of the eyewall region. Prior to analysis, a 20 km filter is applied to the vertical velocity, thermodynamic, and liquid water profiles in order to remove the "more balanced", slowly-evolving mesoscale structure from the transient, unbalanced convective scale features.
The observations indicate that a typical convective-scale eyewall updraft increases magnitude with height and is positively buoyant despite water-loading. Use of the vertical profile of median buoyancy in a simple updraft model reveals that observed vertical motions are much smaller than one would expect from pure buoyancy forcing, suggesting the the vertical perturbation pressure gradient force acts to weaken the updrafts. Buoyant updraft cores were found to occupy less than 5% of the eyewall region but accomplish 25-50% of the total net vertical mass transport. This percentage tended to increase with height, suggesting that buoyant convective-scale updraft cores play an important role in the secondary circulation.
Current theories that address hurricane evolution and vertical motions within the eyewall will be discussed in the context of the observational findings.
Session 17A, Tropical Cyclone Observations and Structure VI(Parallel with Sessions 17B and 17C)
Friday, 3 May 2002, 11:00 AM-12:30 PM
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