Drag Coefficient and Its Sea State Dependence under Tropical Cyclones
Date of Original Version
The drag coefficient under tropical cyclones and its dependence on sea states are investigated by combining upper-ocean current observations [using electromagnetic autonomous profiling explorer (EM-APEX) floats deployed under five tropical cyclones] and a coupled ocean–wave (Modular Ocean Model 6–WAVEWATCH III) model. The estimated drag coefficient averaged over all storms is around 2–3 3 1023 forwindspeedsof25–55 m s21.Whilethedragcoefficient weakly depends on wind speed in this wind speed range, it shows stronger dependence on sea states. In particular, it is signif-icantly reduced when the misalignment angle between the dominant wave direction and the wind direction exceeds about 458, a feature that is underestimated by current models of sea state–dependent drag coefficient. Since the misaligned swell is more common in the far front and in the left-front quadrant of the storm (in the Northern Hemisphere), the drag coefficient also tends to be lower in these areas and shows a distinct spatial distribution. Our results therefore support ongoing efforts to develop and implement sea state–dependent parameterizations of the drag coefficient in tropical cyclone conditions.
Publication Title, e.g., Journal
Journal of Physical Oceanography
Zhou, Xiaohui, Tetsu Hara, Isaac Ginis, Eric D’asaro, Je Yuan Hsu, and Brandon G. Reichl. "Drag Coefficient and Its Sea State Dependence under Tropical Cyclones." Journal of Physical Oceanography 52, 7 (2022). doi: 10.1175/JPO-D-21-0246.1.