Air-sea enthalpy and momentum exchange at major hurricane wind speeds
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Authors
Bell, Michael M.
Subjects
Air-sea interaction
tropical cyclones
surface fluxes
drag coefficient
CBLAST
tropical cyclones
surface fluxes
drag coefficient
CBLAST
Advisors
Montgomery, Michael
Date of Issue
2010-06
Date
June 2010
Publisher
Monterey, California. Naval Postgraduate School
Language
Abstract
Air--sea exchanges of heat and momentum are important elements in understanding and skillfully predicting tropical cyclone intensity, but the magnitude of the corresponding wind-speed dependent bulk exchange coefficients is largely unknown at major hurricane wind speeds greater than 50 m s-1. Since direct turbulent flux measurements in these conditions are extremely difficult, the momentum and enthalpy fluxes were alternatively deduced via axisymmetric angular momentum and total energy budgets. A comprehensive error analysis was performed using both idealized numerical simulations to quantify and mitigate potentially significant uncertainties resulting from unresolved budget terms and observational errors. An analysis of six missions from the 2003 CBLAST field program in major hurricanes Fabian and Isabel was conducted using a new variational technique. This analysis indicates a near-surface mean drag coefficient (CD) of 2.4x10-3 with a 46% standard deviation and a mean enthalpy coefficient (CK) of 1.0x10-3 with a 40% standard deviation for wind speeds between 52 and 72 m s-1. These are the first known estimates of CK and the ratio of enthalpy to drag coefficient (CK/CD) in major hurricanes. The results suggest that there is no significant change in the magnitude of the bulk exchange coefficients estimated at minimal hurricane wind speeds, and the ratio CK/CD is likely less than 0.75 for wind speeds greater than 50 m s-1.
Type
Thesis
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Format
xx, 133 p. : ill. (some col.) ; 28 cm.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.