FLUX MEASUREMENTS FROM A SWATH SHIP IN SWADE

The Surface Wave Dynamics Experiment (SWADE) took place east of the U. S. Coast in the winter of 1990-1991. A major objective of the research program is to refine our understanding of the relationship between fl uxes to the sea surface and the sea state as determined from direction al wave spectra. Simultaneous measurements of turbulent fluxes of mass , momentum and energy between sea and air, with the directional wave s pectra, were required to meet this objective. In this short article we describe the process of obtaining turbulent flux measurements from a small water-plane-area twin hull (SWATH) ship. We measured turbulent f luxes of momentum, heat and water vapor from a tall mast at the bow of the SWATH ship Frederick G. Creed by the eddy correlation method, whi le the ship was moving into the wind. Directional wave spectra were ob tained from a wave staff array ahead of the bow of the ship. The motio n of the ship was recorded and a coordinate rotation was performed for each data sample. After all instrument response and motion correction s have been accounted for, we compare our calculated turbulent fluxes with values computed from another standard method, viz. the inertial d issipation method. This approach is not susceptible to platform motion but relies on assumptions that are not always valid. However, the two methods agree on average within 12%, 20% and 31% for momentum, water vapor and heat fluxes, respectively.