A near-surface microstructure sensor system used during TOGA COARE. Part II: Turbulence measurements

Abstract

New techniques developed for near-surface turbulence measurements during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) employ a difference in spatial scales of turbulence and surface waves. According to this approach, high relative speed of the measurements provides separation of the turbulence and surface wave signals. During the TOGA COARE field studies, high-resolution probes of pressure, temperature, conductivity, fluctuation velocity, and acceleration were mounted on the bow of the vessel at a 1.7-m depth in an undisturbed region ahead of the moving vessel. The localization in narrow frequency bands of the vibrations of the bow sensors allows accurate calculation of the dissipation rate. A coherent noise reduction algorithm effectively removes vibration contamination of the velocity dataset. Due to the presence of surface waves and the associated pitching of the vessel, the bow probes 'scanned' the near-surface layer of the ocean. Contour plots calculated using the bow signals provide a spatial context for the analysis of near-surface turbulence. A fast-moving free-rising profiler equipped by similar probes sampled the near-surface turbulence during stations. Theory of the three-component electromagnetic velocity sensor and examples of data obtained by bow sensors and free-rising profiler are also presented in this paper.