Jonah V. Steinbuck

Evidence for Submesoscale Barriers to Horizontal Mixing in the Ocean from Current Measurements and Aerial Photographs

Abstract Ocean submesoscale (∼2–20 km) mixing processes play a major role in ocean dynamics, in physical–biological interactions (e.g., in the dispersion of larvae), and in the dispersion of pollutants. In this paper, horizontal mixing on a scale of a few kilometers is investigated, from observations of surface currents, using highly resolved (300 m) high-frequency radar. These results show the complexity of ocean mixing on scales of a few kilometers and the existence of temporary barriers to mixing that can affect the dispersion of biological materials and pollutants. These barriers are narrow [O(100 m)] and can survive for a few days. The existence of these barriers is supported in simultaneous aerial photographs. The barriers observed here may require a new approach to the way horizontal mixing is parameterized in ocean and climate models.

An Evaluation of χT Estimation Techniques: Implications for Batchelor Fitting and ε

Abstract Techniques for the accurate estimation of the dissipation rate of temperature variance χT from temperature microstructure measurements are synthesized and evaluated. The techniques focus on the treatment of contamination in the integration of the vertical temperature gradient spectrum. The essential improvements come from estimating χT from the wavenumber domain in which the signal exceeds the noise and from reconstructing unresolved wavenumber contributions using the best-fit Batchelor spectrum. The improvement in the estimates of χT results in better Batchelor fits and more robust estimates of the dissipation rate of turbulent kinetic energy e. High correlations of independent measurements of χT and e from two collocated FP07 thermistors demonstrate the value of the techniques and highlight the improvements at the low end of the resolvable ranges of χT and e.

An Autonomous Open-Ocean Stereoscopic PIV Profiler

Abstract Over the past decade, a novel free-fall imaging profiler has been under development at the Scripps Institution of Oceanography to observe and quantify biological and physical structure in the upper 100 m of the ocean. The profiler provided the first detailed view of microscale phytoplankton distributions using in situ planar laser-induced fluorescence. The present study examines a recent incarnation of the profiler that features microscale turbulent flow measurement capabilities using stereoscopic particle image velocimetry (PIV). As the profiler descends through the water column, a vertical sheet of laser light illuminates natural particles below the profiler. Two sensitive charge-coupled device (CCD) cameras image a 25 cm × 25 cm × 0.6 cm region at a nominal frame rate of 8 Hz. The stereoscopic camera configuration allows all three components of velocity to be measured in the vertical plane with an average spatial resolution of approximately 3 mm. The performance of the PIV system is evaluated ...

Estimation of In Situ 3-D Particle Distributions From a Stereo Laser Imaging Profiler

In this paper, an image processing system for estimating 3-D particle distributions from stereo light scatter images is described. The system incorporates measured, three-component velocity data to mitigate particle blur associated with instrument motion. An iterative background estimation algorithm yields a local threshold operator that dramatically reduces bias in particle counts over the full image field. Algorithms are tested on simulated particle distributions and data from an open-ocean profile collected near the Santa Barbara Channel Islands, CA. They yield over a 50% reduction in root-mean-squared error in particle size estimates, and a 30% reduction in the magnitude of the motion blur point spread function. In situ particle distributions are estimated and compared to several models. It is demonstrated that quantitative, 3-D particle distributions can be accurately estimated from these data for particles with diameter larger than 4 pixels (0.8 mm).