ALBERT

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in St. Laurent, L., Ijichi, T., Merrifield, S. T., Shapiro, J., & Simmons, H. L. Turbulence and vorticity in the Wake of Palau. Oceanography, 32(4), (2019): 102-109, doi: 10.5670/oceanog.2019.416.

Description: The interaction of flow with steep island and ridge topography at the Palau island chain leads to rich vorticity fields that generate a cascade of motions. The energy transfer to small scales removes energy from the large-scale mean flow of the equatorial current systems and feeds energy to the fine and microstructure scales where instability mechanisms lead to turbulence and dissipation. Until now, direct assessments of the turbulence associated with island wakes have received only minimal attention. Here, we examine data collected from an ocean glider equipped with microstructure sensors that flew in the island wake of Palau. We use a combination of submesoscale modeling and direct observation to quantify the relationship between vorticity and turbulence levels. We find that direct wind-driven mixing only accounts for about 10% of the observed turbulence levels, suggesting that most of the energy for mixing is extracted from the shear associated with the vorticity field in the island’s wake. Below the surface layer, enhanced turbulence correlates with the phase and magnitude of the relative vorticity and strain levels of the mesoscale flow.

Description: We thank the Palau National Government for permission to carry out the research in Palau. We also thank the US Office of Naval Research for supporting this work. We especially thank Pat and Lori Colin of the Coral Reef Research Foundation and their team for accommodating our research team in Koror, Palau, and running vessel operations in support of glider deployments and recoveries. Sean Whelan of the Woods Hole Oceanographic Institution and Lance Braasch of Scripps Institution of Oceanography provided technical support in the field. Funding for the development of HYCOM has been provided by the National Ocean Partnership Program and the Office of Naval Research. Data assimilative products using HYCOM are funded by the US Navy. Computer time was made available by the Department of Defense High Performance Computing Modernization Program. The output is publicly available at https://www.hycom.org/.

Description: Author Posting. © The Oceanography Society, 2017. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 30, no. 2 (2017): 116–125, doi:10.5670/oceanog.2017.231.

Description: As autonomous sampling technologies have matured, ocean sensing concepts with long histories have migrated from their traditional ship-based roots to new platforms. Here, we discuss the case of ocean microstructure sensing, which provides the basis for direct measurement of small-scale turbulence processes that lead to mixing and buoyancy flux. Due to their hydrodynamic design, gliders are an optimal platform for microstructure sensing. A buoyancy-driven glider can profile through the ocean with minimal vibrational noise, a common limitation of turbulence measurements from other platforms. Moreover, gliders collect uncontaminated data during both descents and ascents, permitting collection of near-surface measurements unattainable from ship-based sensing. Persistence and the capability to sample in sea states not feasible for deck-based operations make glider-based microstructure sampling a profoundly valuable innovation. Data from two recent studies illustrate the novel aspects of glider-based turbulence sensing. Surface stable layers, characteristic of conditions with incoming solar radiation and weak winds, exemplify a phenomenon not easily sampled with ship-based methods. In the North Atlantic, dissipation rate measurements in these layers revealed unexpected turbulent mixing during times of peak warming, when enhanced stratification in a thin layer led to an internal wave mode that received energy from the deeper internal wave field of the thermocline. Hundreds of profiles were obtained in the Bay of Bengal through a barrier layer that separates a strongly turbulent surface layer from a surprisingly quiescent interior just 20 m below. These studies demonstrate the utility of buoyancy-driven gliders for collecting oceanic turbulence measurements.

Description: We thank the US Office of Naval Research (ONR) for supporting the development of autonomous glider systems and the integration effort to incorporate microstructure sensing. The National Science Foundation supported the SPURS microstructure glider effort. ONR supported for the glider program in the Bay of Bengal.