Download files
Abstract
This thesis is a study of the air-sea fluxes of momentum, sensible heat and latent heat.
Fluxes are estimated using the covariance, COARE2.6b bulk flux algorithm, and inertial dissipation methods.
The bulk algorithm is validated against the covariance fluxes for the first time in a light-wind, shallow tropical sea, with strong atmospheric instability and low sea state conditions.
The removal of ship motion contamination is investigated.
This is the first study to quantify the errors associated with corrections for ship motion contamination, and the effects of motion contamination on the covariance calculated heat fluxes.
Flow distortion is investigated.
Bulk transfer coefficients and roughness lengths are computed and related to the sea state.
Ship motion contamination is successfully removed in 86% of the runs.
Error analysis of the motion removal algorithm indicates maximum uncertainties of 15% in the wind fluctuations, and 0.002 N/m/m for the wind stress. Motion correction changes the stress by more than 15% in half of the runs analysed.
The ship is found to accelerate the mean air flow and deflect it above the horizontal. A correction is developed for the air flow acceleration.
The scalar fluxes show good agreement on average for all the methods.
As wind speed approaches zero, covariance wind stress is significantly larger than the bulk and inertial dissipation derived wind stress.
The non-zero covariance wind stress is reflected in the drag coefficient, CdN10, and momentum roughness length, z0, which are much larger than the parameterisations used in the bulk algorithm.
The MCTEX CdN10, wind speed (u10N) relation is
1000 x Cd10N = 1.03 + 7.88/(u10N)^2 0.8 < u10N < 7.5 m/s
z0 is primarily a function of wind speed rather than sea state, with largest roughness lengths occurring as wind speed approaches zero. This relation is used in the bulk algorithm, yielding good agreement between covariance and bulk derived wind stress.
A new parameterisation for the effects of gustiness, based on wind variance is developed. This brings the bulk wind stress into agreement with the covariance derived wind stress.