Fetch Limited Drag Coefficients

Measurements made at a tower located 2 km off the coast of Denmark inshallow water during the Risø Air Sea Experiment (RASEX) are analyzedto investigate the behaviour of the drag coefficient in the coastal zone.For a given wind speed, the drag coefficient is larger during conditions ofshort fetch (2-5 km) off-shore flow with younger growing waves than it isfor longer fetch (15-25 km) on-shore flow. For the strongest on-shorewinds, wave breaking enhances the drag coefficient. Variation of the neutral drag coefficient in RASEX is dominated byvariation of wave age, frequency bandwidth of the wave spectra and windspeed. The frequency bandwidth is proportional to the broadness of the waveheight spectra and is largest during conditions of light wind speeds. Usingthe RASEX data, simple models of the drag coefficient and roughness length are developed in terms of wind speed, wave age and bandwidth. An off-shoreflow model of the drag coefficient in terms of nondimensional fetch isdeveloped for situations when the wave state is not known.

[1]  H. Charnock.  Wind stress on a water surface , 1955 .

[2]  G. Geernaert.  Drag coefficient modeling for the near coastal zone , 1988 .

[3]  T. E. Nordeng.  On the wave age dependent drag coefficient and roughness length at sea , 1991 .

[4]  Stuart D. Smith.  Wind Stress and Heat Flux over the Ocean in Gale Force Winds , 1980 .

[5]  P. A. Sheppard,et al.  Studies of turbulence in the surface layer over water (Lough Neagh). Part I. Instrumentation, programme, profiles , 1972 .

[6]  Dean Vickers,et al.  Quality Control and Flux Sampling Problems for Tower and Aircraft Data , 1997 .

[7]  E. F. Bradley,et al.  Bulk parameterization of air‐sea fluxes for Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment , 1996 .

[8]  J. Garratt.  Review of Drag Coefficients over Oceans and Continents , 1977 .

[9]  S. Kitaigorodskii.  The physics of air-sea interaction , 1973 .

[10]  Frans T. M. Nieuwstadt,et al.  Temperature measurement with a sonic anemometer and its application to heat and moisture fluxes , 1983 .

[11]  Jørgen Højstrup,et al.  The Vindeby project: A description , 1994 .

[12]  W. K. Melville,et al.  On the separation of air flow over water waves , 1976, Journal of Fluid Mechanics.

[13]  Jin Wu,et al.  Wind-Stress coefficients over Sea surface near Neutral Conditions—A Revisit , 1980 .

[14]  R. Long,et al.  Array measurements of atmospheric pressure fluctuations above surface gravity waves , 1981, Journal of Fluid Mechanics.

[15]  W. Large,et al.  Open Ocean Momentum Flux Measurements in Moderate to Strong Winds , 1981 .

[16]  W. Perrie,et al.  Fetch Relations for Wind-Generated Waves as a Function of Wind-Stress Scaling , 1990 .

[17]  Karl F. Rieder.  ANALYSIS OF SEA-SURFACE DRAG PARAMETERIZATIONS IN OPEN OCEAN CONDITIONS , 1997 .

[18]  C. Paulson.  The Mathematical Representation of Wind Speed and Temperature Profiles in the Unstable Atmospheric Surface Layer , 1970 .

[19]  Michael H. Freilich,et al.  Nonlinear effects on shoaling surface gravity waves , 1984, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[20]  W. A. Oost,et al.  The roughness of wind waves , 1991 .

[21]  E. G. Banke,et al.  Variation of the sea surface drag coefficient with wind speed , 1975 .

[22]  Kristina B. Katsaros,et al.  Incorporation of Stratification Effects on the Oceanic Roughness Length in the Derivation of the Neutral Drag Coefficient , 1986 .

[23]  M. Banner.  The influence of wave breaking on the surface pressure distribution in wind—wave interactions , 1990, Journal of Fluid Mechanics.

[24]  S. Larsen,et al.  Measurements of the wind stress, heat flux, and turbulence intensity during storm conditions over the North Sea , 1987 .

[25]  R. Weller,et al.  Observed directional characteristics of the wind, wind stress, and surface waves on the open ocean , 1994 .

[26]  L. Hasse,et al.  Sea surface wind stress and drag coefficients: The hexos results , 1992 .

[27]  M. Donelan,et al.  On the Dependence of Sea Surface Roughness on Wave Development , 1993 .

[28]  Yoshiaki Toba,et al.  A Parameter Describing Overall Conditions of Wave Breaking, Whitecapping, Sea-Spray Production and Wind Stress , 1986 .

[29]  Dean Vickers,et al.  Sea surface drag coefficients in the Risø Air Sea Experiment , 1996 .

[30]  G. Geernaert,et al.  Variation of the drag coefficient and its dependence on sea state , 1986 .

[31]  Michael H. Freilich,et al.  Observations of Nonlinear Effects in Directional Spectra of Shoaling Gravity Waves , 1990 .

[32]  U. Inan.  Gyroresonant pitch angle scattering by coherent and incoherent whistler mode waves in the magnetosphere , 1987 .

[33]  Judith A. Curry,et al.  Determination of surface turbulent fluxes over leads in Arctic , 1997 .

[34]  R. W. Stewart.  The air-sea momentum exchange , 1974 .

[35]  Michael Tjernström,et al.  The Near-Neutral Marine Atmospheric Boundary Layer with No Surface Shearing Stress: A Case Study , 1994 .

[36]  Stuart D. Smith.  Coefficients for sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature , 1988 .