Journal
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 127, Issue 9, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2021JC018360
Keywords
tropical cyclone; drag coefficient; different quadrant; asymmetry; coastal ocean; offshore platform
Categories
Funding
- Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao) [2022QNLM010102]
- Basic Scientific Fund for National Public Research Institutes of China [2022Q01]
- National Natural Science Foundation of China [41821004, 42276024]
- NOAA [NA19OAR0220186, NA14NWS4680028, NA21OAR4590370]
- NSF [AGS-1822128]
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This study investigates the behavior of drag coefficient (CD ${C}_{\mathrm{D}}$) in two different motion-relative quadrants of Typhoon Mujigae (2015) through flux observations. The observations reveal that the variation of CD ${C}_{\mathrm{D}}$ is closely related to the location relative to the tropical cyclone (TC) center. The CD ${C}_{\mathrm{D}}$ presents an enhancement when the typhoon is away from the observational site and the distribution of CD ${C}_{\mathrm{D}}$ is asymmetric. CD ${C}_{\mathrm{D}}$ tends to level off and even attenuate with the increase of wind speed.
The behavior of drag coefficient (CD ${C}_{\mathrm{D}}$) 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 CD ${C}_{\mathrm{D}}$ is closely related to the location relative to the tropical cyclone (TC) center. The CD ${C}_{\mathrm{D}}$ presents an enhancement when the typhoon is away from the observational site. The spatial distribution of CD ${C}_{\mathrm{D}}$ on the periphery of a TC is asymmetric, and the CD ${C}_{\mathrm{D}}$ 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 CD ${C}_{\mathrm{D}}$ can be explained by the differences in wave properties between the two quadrants. CD ${C}_{\mathrm{D}}$ is smaller in cross-swell conditions than that in the along-wind wave conditions. Observations also confirm that CD ${C}_{\mathrm{D}}$ tends to level off and even attenuate with the increase of wind speed, and the critical wind speed for CD ${C}_{\mathrm{D}}$ saturation over the coastal region (similar to 20 m/s) is much lower than that over the open ocean (similar to 30 m/s). The observational spatial distribution of CD ${C}_{\mathrm{D}}$ 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.
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