A Near-Surface Microstructure Sensor System Used During TOGA COARE. Part II: Turbulence Measurements

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, highresolution 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

A Near-Surface Microstructure Sensor System Used During TOGA COARE. Part I: Bow Measurements.

High-resolution probes mounted on the bow of the vessel at a 1.7-m depth in an undisturbed region ahead of the moving vessel were used for microstructure and turbulence measurements in the near-surface layer of the ocean during TOGA COARE. The probes measured temperature, conductivity, pressure, three-component fluctuation velocity, and two components of acceleration. Accumulation of large amounts of high-quality nearsurface data poses a difficult challenge, and deployment from the bow of a ship, such as is done with these sensors, requires rugged, well-calibrated, and low-noise sensors. The heaving motion of the ship that causes the sensors to break through the surface requires data processing algorithms unique to this application. 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. Combining the bow sensor’s signals with the ship’s thermosalinograph pumping water from 3-m depth resulted in the near-surface dataset with both fine temporal/spatial resolution and high absolute accuracy. Contour plots calculated using the bow signals reveal the spatial structure of the diurnal thermocline and rain-formed halocline. The localization in narrow frequency bands of the vibrations of the bow sensors allows calculation of dissipation rates. The characteristics of the sensors and the data processing algorithms related to the periodic surface penetration by the sensors are discussed in this paper