Title: Observed drag coefficients in high winds in the near offshore of the South China Sea

Abstract

This paper investigates the relationships between friction velocity, 10 m drag coefficient, and 10 m wind speed using data collected at two offshore observation towers (one over the sea and the other on an island) from seven typhoon episodes in the South China Sea from 2008 to 2014. The two towers were placed in areas with different water depths along a shore-normal line. The depth of water at the tower over the sea averages about 15 m, and the depth of water near the island is about 10 m. The observed maximum 10 min average wind speed at a height of 10 m is about 32 m s⁻¹. Momentum fluxes derived from three methods (eddy covariance, inertial dissipation, and flux profile) are compared. The momentum fluxes derived from the flux profile method are larger (smaller) over the sea (on the island) than those from the other two methods. The relationship between the 10 m drag coefficient and the 10 m wind speed is examined by use of the data obtained by the eddy covariance method. The drag coefficient first decreases with increasing 10 m wind speed when the wind speeds are 5–10 m s⁻¹, then increases and reaches a peakmore » value of 0.002 around a wind speed of 18 m s⁻¹. The drag coefficient decreases with increasing 10 m wind speed when 10 m wind speeds are 18–27 m s⁻¹. A comparison of the measurements from the two towers shows that the 10 m drag coefficient from the tower in 10 m water depth is about 40% larger than that from the tower in 15 m water depth when the 10 m wind speed is less than 10 m s⁻¹. Above this, the difference in the 10 m drag coefficients of the two towers disappears.« less

Authors:

Bi, Xueyan ^[1]; Liu, Yangan ^[2]; Gao, Zhiqiu ^[3]; Liu, Feng ^[4]; Song, Qingtao ^[5]; Huang, Jian ^[6]; Huang, Huijun ^[6]; Mao, Weikang ^[6]; Liu, Chunxia ^[6]

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+ Show Author Affiliations

1. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Chemistry; Guangzhou Institute of Tropical and Marine Meteorology, Guangdong (China); Brookhaven National Lab. (BNL), Upton, NY (United States)
2. Brookhaven National Lab. (BNL), Upton, NY (United States)
3. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Chemistry
4. Univ. of Illinois at Urban-Champaign, Champaign, IL (United States)
5. National Satellite Ocean Application Service, Beijing (China); Key Lab. of Space Ocean Remote Sensing and Application, Beijing (China)
6. Guangzhou Institute of Tropical and Marine Meteorology, Guangdong (China)

Publication Date:

Tue Jul 14 00:00:00 EDT 2015

Research Org.:

Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1201368

Report Number(s):

BNL-108210-2015-JA
Journal ID: ISSN 2169-897X; R&D Project: 2016-BNL-EE631EECA-Budg; KP170302

Grant/Contract Number:  

SC00112704

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research: Atmospheres

Additional Journal Information:

Journal Volume: 120; Journal Issue: 13; Journal ID: ISSN 2169-897X

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES