Publication Date:
2019
Description:
Abstract
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 twelve EM‐APEX floats beneath the forward half of five TCs. Combining estimates of τ and aircraft measurements of winds U10, the downwind drag coefficient
and the angle ϕ clockwise orientation from U10 to τ are computed. At|U10|= 25–40 m s–1,
and ϕ vary over (0.8–3.1) ×10‐3 and ‐15–40°, respectively. A new non‐dimensional parameter ‘effective wind duration’, a function of|U10|, storm translation speed, and positions in TCs, predicts
to within 25%. The largest
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.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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