Turbulent mixing in a tidal channel
Date
1997
Authors
Huang, Dai Yan
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Abstract
During a joint collaborative experiment between September 19 and 30, 1994, a novel microstructure instrument (TAMI), which was attached to the channel bottom on a mooring line and measured changes in horizontal flows, successfully measured microstructure, fine-structure and current at 15 m above the bottom in Cordova Channel. The channel is a minor passage connecting the Pacific Ocean and the Strait of Georgia. The other main instruments involved in the experiment were an acoustic Doppler current profiler (ADCP), an acoustic scintillation system, CTD profiler and a meteorology station.
The flow of the channel was mainly tidal. The tidal components explained slightly more than 91 % of the variance of the measured current, and the residual current which represented 2-D horizontal eddies and accounted for about 10% of tidal variance. The water became warmer and fresher during the experiment. With TAMI, the salinity record showed modulation by the tide while the temperature record did not exhibit a clear tidal signal. The water was fairly well mixed during strong ebbing, more stratified during the floods and became unstable occasionally near the turning of the tide. The effect of wind stress at 15 m depth was much weaker than that from the local bottom stress.
The spectra of the velocity and temperature fluctuat ions, in water, all had a -5/3 slope in the inertial-subrange regardless of the level of stratification in the channel. Thus, the finding that the slope of velocity and temperature spectra are affected by stratification in Gargett et al. (1984) and Gargett (1985) is not universal and may be more due to the physics of decaying turbulence than to stratification itself. The two universal functions (A2 and F33) were statistically identical in the inertial-subrange and even no evident influence of stratification on vertical spectrum.