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Boundary Layer Structure and Dynamics
Principal Investigator : Mark Powell
Group Members :
Peter Dodge
Collaborators :
Gary Barnes (U. Hawaii)
Tim Reinhold (Clemson U.)
Peter Vickery (U. Western Ontario)
Kurt Gurley (UF)
Forrest Masters (UF)
Objective :
This project focuses assessing boundary layer structure and
air-sea flux behavior in tropical cyclones. A large database of
GPS sonde profiles provides a rich source of information to
determine bulk profile and surface layer characteristics
needed to understand physical processes in the hurricane
boundary layer.
Methods :
Invoking similarity and ergodicity, large numbers of profiles in similar
conditions are averaged to provide measurements of surface roughness and drag
coefficient. The values are then investigated for behavior as a function of
wind speed, storm relative location, and water depth.
Findings :
The drag coeficient exhibits an initial increase with wind speed for winds up
to hurricane force followed by a decrease as winds continue to increase. When
broken down by radius, this behavior is confined to radii beyond 30 km while
inner radii exhibit relatively small variations in drag with wind speed. When
broken down by storm-relative azimuth, the drag coefficient on the front left
side of the storm shows much larger values than the other storm quadrants.
A paper describing roughness and drag coefficient behavior in hurricanes
published in Nature.
References :
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Powell, M.D., P.J. Vickery, and T.A. Reinhold, 2003:
"Reduced drag coefficient for high wind speeds in tropical
cyclones" Nature vol 422, March 20 pp.279-283
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Wright, C.W., E.J. Walsh, D. Vandemark, W.B. Krabill, A.W.
Garcia, S.H. Houston, M.D. Powell, P.G. Black, and F.D. Marks,
2001: "Hurricane directional wave spectrum spatial variation in
the open ocean" Journal of Physical Oceanography, 31(8):2472-2488.
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Barnes, G. M. and M. D. Powell, 1995: Evolution of the inflow
boundary layer of Hurricane Gilbert (1988). Mon. Wea. Rev., 123,
2348-2368.
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Powell, M. D., 1990: Boundary layer structure and dynamics in
outer hurricane rainbands. Part I: Mesoscale rainfall and
kinematic structure. Mon. Wea.Rev., 118, 891-917
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Powell, M. D., 1990: Boundary layer structure and dynamics in
outer hurricane rainbands. Part II: Downdraft modification and
mixed layer recovery. Mon. Wea. Rev., 118, 918-938
FY04 proposed milestones:
Extend methods to analyze heat and moisture transfer at the ocean
surface, investigate the behavior of sea surface roughness in shallow
coastal waters and strong winds.
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Last modified: 5/16/2003
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