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Scaling of Drag Coefficients Under Five Tropical Cyclones
Author(s) -
Hsu JeYuan,
Lien RenChieh,
D'Asaro Eric A.,
Sanford Thomas B.
Publication year - 2019
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl081574
Subject(s) - drag coefficient , tropical cyclone , storm , drag , atmospheric sciences , scaling , meteorology , clockwise , wind speed , forcing (mathematics) , physics , geology , environmental science , climatology , mechanics , geometry , amplitude , mathematics , quantum mechanics
The drag coefficient, often used to parameterize the surface wind stress τ, beneath tropical cyclones (TCs) is a critical but poorly known factor controlling TC intensity. Here, τ is estimated using current measurements taken by 12 Electromagnetic Autonomous Profiling Explorer floats beneath the forward half of five TCs. Combining estimates of τ and aircraft measurements of winds U 10 , the downwind drag coefficientC ∥ ~ and the angle ϕ clockwise orientation from U 10 to τ are computed. At | U 10 | = 25–40 m/s,C ∥ ~ and ϕ vary over (0.8–3.1) × 10 −3 and −15–40°, respectively. A new nondimensional parameter “effective wind duration,” a function of | U 10 |, storm translation speed, and positions in TCs, predictsC ∥ ~ to within 25%. The largestC ∥ ~ and smallest ϕ occur at high winds, in the forward right quadrant of fast‐moving storms. These dependences are explained by variations in surface wave age and breaking under different wave forcing regimes.