A New Drag Relation for Aerodynamically Rough flow over the Ocean

作者：Andreas Edgar L^*; Mahrt Larry; Vickers Dean

来源：Journal of the Atmospheric Sciences, 2012, 69(8): 2520-2537.

DOI：10.1175/JAS-D-11-0312.1

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: %26lt;br%26gt;u(*) = 0.0583U(N10) - 0.243. %26lt;br%26gt;Here u(*) is the measured friction velocity, and U-N10 is the neutral-stability wind speed at a reference height of 10 m. This relation is fitted to U-N10 values between 9 and 24 m s(-1). A drag relation formulated as u(*) versus U-N10 has several advantages over one formulated in terms of C-DN10 = (u(*)/U-N10)(2). First, the multiplicative coefficient on U-N10 has smaller experimental uncertainty than do determinations of C-DN10. Second, scatterplots of u(*) versus U-N10 are not ill posed when U-N10 is small, as plots of C-DN10 are; u(*)-U-N10 plots presented here suggest aerodynamically smooth scaling for small U-N10. 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 C-DN10 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 C-DN10 results simply from known processes that influence wind-wave coupling.

• 出版日期2012-8