Estimates of Surface Wind Stress and Drag Coefficients in Typhoon Megi
Abstract
Estimates of drag coefficients beneath Typhoon Megi (2010) are calculated from roughly hourly velocity profiles of three EM-APEX floats, air launched ahead of the storm, and from air-deployed dropsondes measurements and microwave estimates of the 10-m wind field. The profiles are corrected to minimize contributions from tides and low-frequency motions and thus isolate the current induced by Typhoon Megi. Surface wind stress is computed from the linear momentum budget in the upper 150 m. Three-dimensional numerical simulations of the oceanic response to Typhoon Megi indicate that with small corrections, the linear momentum budget is accurate to 15% before the passage of the eye but cannot be applied reliably thereafter. Monte Carlo error estimates indicate that stress estimates can be made for wind speeds greater than 25 m s−1; the error decreases with greater wind speeds. Downwind and crosswind drag coefficients are computed from the computed stress and the mapped wind data. Downwind drag coefficients increase to 3.5 ± 0.7 × 10−3 at 31 m s−1, a value greater than most previous estimates, but decrease to 2.0 ± 0.4 × 10−3 for wind speeds > 45 m s−1, in agreement with previous estimates. The crosswind drag coefficient of 1.6 ± 0.5 × 10−3 at wind speeds 30–45 m s−1 implies that the wind stress is about 20° clockwise from the 10-m wind vector and thus not directly downwind, as is often assumed.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 01, 2017
- Source ID
- 10.1175/jpo-d-16-0069.1
Entities
People
- Eric A. D'Asaro
- Je-yuan Hsu
- Ren-Chieh Lien
- Thomas B. Sanford
Organizations
- Office of Naval Research
- University of Washington