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Typhoon air‐sea drag coefficient in coastal regions
Author(s) -
Zhao ZhongKuo,
Liu ChunXia,
Li Qi,
Dai GuangFeng,
Song QingTao,
Lv WeiHua
Publication year - 2015
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc010283
Subject(s) - typhoon , wind speed , drag coefficient , wind shear , environmental science , meteorology , drag , momentum (technical analysis) , geology , atmospheric sciences , climatology , geography , physics , mechanics , finance , economics
The air‐sea drag during typhoon landfalls is investigated for a 10 m wind speed as high as U 10 ≈ 42 m s −1 , based on multilevel wind measurements from a coastal tower located in the South China Sea. The drag coefficient ( C D ) plotted against the typhoon wind speed is similar to that of open ocean conditions; however, the C D curve shifts toward a regime of lower winds, and C D increases by a factor of approximately 0.5 relative to the open ocean. Our results indicate that the critical wind speed at which C D peaks is approximately 24 m s −1 , which is 5–15 m s −1 lower than that from deep water. Shoaling effects are invoked to explain the findings. Based on our results, the proposed C D formulation, which depends on both water depth and wind speed, is applied to a typhoon forecast model. The forecasts of typhoon track and surface wind speed are improved. Therefore, a water‐depth‐dependence formulation of C D may be particularly pertinent for parameterizing air‐sea momentum exchanges over shallow water.