Analysis of Wave-Induced Errors in Turbulent Flux Measurements.
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Near surface measurements of turbulent temperature and velocity fluctuations in the ocean are obscured by relatively much larger ordered fluctuations due to surface gravity waves. Analysis of measured velocity signals in the near surface region indicated that the ratio of turbulent to wave-induced kinetic energy was consistently less than .01. To a first approximation, wave-induced fluctuations should not contribute to turbulent transport. However, small instrument errors due to misalignment, phase response, or directional response may cause significant wave-induced error in direct flux measurements. The effect on turbulent flux measurements of misalignment of the velocity sensors was examined. It was found that misalignment resulted in apparent phase shifts in the measured wave-induced signals, causing erroneous contributions to the calculated flux. For alignment errors of 3.6, the error in calculated momentum and heat fluxes could have been up to 500 and 110, respectively. Momentum flux measurements made in deep water with respect to the length of surface waves were found to be less sensitive to alignment errors. The errors in this case were functions of the alignment of the flowmeter axes with the predominant wave direction.
- Physical and Dynamic Oceanography
- Fluid Mechanics