Observed Drag Coefficient Asymmetry in a Tropical Cyclone
Sheng Chen, Fangli Qiao, Jun A. Zhang, Yuhuan Xue, Hongyu Ma, Siyu Chen
Abstract
Abstract The behavior of drag coefficient ( ) in two different motion‐relative quadrants of Typhoon Mujigae (2015) is investigated through the flux observations conducted on a fixed platform over the coastal region in the northern South China Sea. Observations reveal that the variation of is closely related to the location relative to the tropical cyclone (TC) center. The presents an enhancement when the typhoon is away from the observational site. The spatial distribution of on the periphery of a TC is asymmetric, and the in the right rear quadrant is much larger than that in the right front quadrant for the same wind speed range. This asymmetric distribution of can be explained by the differences in wave properties between the two quadrants. is smaller in cross‐swell conditions than that in the along‐wind wave conditions. Observations also confirm that tends to level off and even attenuate with the increase of wind speed, and the critical wind speed for saturation over the coastal region (∼20 m/s) is much lower than that over the open ocean (∼30 m/s). The observational spatial distribution of in TC quadrants not only improves our understanding on the air‐sea momentum flux but also provides a potential solution for the long‐standing scientific bottleneck on TC intensity forecasting.