The sea surface roughness z0 is usually determined from friction velocity u* with the Charnock relation as z0=zchu*/g, where g is the gravitational acceleration and zch an empirical parameter, which was meant to be a constant, but turned out to be site specific for sites with coastal influence. Several attempts to improve this relation aim on finding a power law between a non-dimensional sea surface roughness and a non-dimensional group describing the influence of the wave field. The Rodsand field measurement was used to test several proposed relations. A significant correlation with sea surface roughness was found only if wave age, cp/u*, was used as non-dimensional group for the wave field influence, where cp is the velocity of the peak wave component. However, it was also shown that this scaling suffers from the general problems of self-correlation and wind speed dependence. In a test application only a small improvement of the predicted 10 m wind was obtained using this wave age dependent relation. An empirical relation for the dependence of wave age on fetch was used to derive a fetch dependent relation for the sea surface roughness. The 10 m wind speed predicted with this relation was only insignificantly better than with the Charnock equation itself.
[1]
L. Hasse,et al.
Sea surface wind stress and drag coefficients: The hexos results
,
1992
.
[2]
J. Monbaliu.
On the use of the Donelan wave spectral parameter as a measure for the roughness of wind waves
,
1994
.
[3]
S. Larsen,et al.
On the Dependence of Sea Surface Roughness on Wind Waves
,
1998
.
[4]
Description of the Rødsand field measurement
,
2001
.
[5]
N. Ebuchi,et al.
Wave Dependence of Sea-Surface Wind Stress
,
1990
.
[6]
H. Charnock.
Wind stress on a water surface
,
1955
.
[7]
Kimmo K. Kahma,et al.
Reconciling Discrepancies in the Observed Growth of Wind-generated Waves
,
1992
.
[8]
P. K. Taylor,et al.
The Dependence of Sea Surface Roughness on the Height and Steepness of the Waves
,
2001
.