- From almost 7000 near-surface eddy-covariance flux measurements over the sea, the authors deduce a new
air–sea drag relation for aerodynamically rough flow:
u* = 0.0583Uₙ₁₀ 2 0.243.
Here u* is the measured friction velocity, and Uₙ₁₀ is the neutral-stability wind speed at a reference height
of 10 m. This relation is fitted to Uₙ₁₀ values between 9 and 24 m s⁻¹.Adrag relation formulated as u* versus
Uₙ₁₀ has several advantages over one formulated in terms of C𝒹ₙ₁₀ = (u*/Uₙ₁₀)². First, the multiplicative
coefficient on Uₙ₁₀ has smaller experimental uncertainty than do determinations of C𝒹ₙ₁₀. Second, scatterplots
of u* versus Uₙ₁₀ are not ill posed when Uₙ₁₀ is small, as plots of C𝒹ₙ₁₀ are; u*–Uₙ₁₀ plots presented
here suggest aerodynamically smooth scaling for small Uₙ₁₀. Third, this relation depends only weakly on
Monin–Obukhov similarity theory and, consequently, reduces the confounding effects of artificial correlation.
Finally, with its negative intercept, the linear relation produces a C𝒹ₙ₁₀ function that naturally rolls off at
high wind speed and asymptotically approaches a constant value of 3.40 x 10⁻³. Hurricane modelers and
the air–sea interaction community have been trying to rationalize such behavior in the drag coefficient for at
least 15 years. This paper suggests that this rolloff in C𝒹ₙ₁₀ results simply from known processes that
influence wind–wave coupling.
- Andreas, Edgar L, Larry Mahrt, Dean Vickers, 2012: A New Drag Relation for Aerodynamically Rough Flow over the Ocean. Journal of the Atmospheric Sciences, 69, 2520–2537. doi: http://dx.doi.org/10.1175/JAS-D-11-0312.1
|Funding Statement (additional comments about funding)
- The U.S.Office of Naval Research supported this work with AwardN00014-11-1-0073 to NorthWest Research Associates.ONR also supported ELA through the National OceanPartnership Program with Award N00014-10-1-0154 tothe University of Rhode Island, for whom he is a subcontractor.
- This is the publisher’s final pdf.
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