THE TURBULENCE REGIME OF A VERY STABLE MARINE AIR-FLOW WITH QUASI-FRICTIONAL DECOUPLING

Data from an air/sea interaction experiment over the Baltic Sea during conditions with very large land - sea surface temperature contrast ha ve been analyzed. It is found that the measured shearing stress and se nsible heat flux were strongly suppressed compared to what would be ex pected from current theory. Analysis of spectral behavior shows that a strong wind gradient imposed by the presence of a low-level jet at or below 100 m height during about 80% of the time is exerting strong in fluence on the turbulence regime by suppressing low-frequency fluctuat ions. The dissipation length scale was found to equal a new length sca le L-vT which has the vertical velocity standard deviation in the nume rator and the sum of the wind gradient and the Brunt-Vaisala frequency in the denominator. It was also found that the 10 m drag coefficient C-D10 was a strong function of this scale, with small values of L-vT g iving almost zero C-D10 values. Integrating the locally found wind gra dient down to the surface resulted in roughness length values several orders of magnitude less than that valid for a dynamically smooth flow . With turbulence measurements at only one height, 10 m, no conclusive explanation of this anomaly could be given. Observed significant wave height during the experiment was, however, found to be a factor of 2. 5 lower on the average than predicted by current theory.