Coupling of Waves, Turbulence and Thermodynamics Across the Marginal Ice Zone

LONG TERM GOALS: Long term goals are to observe and model processes controlling ice retreat in the marginal ice zone (MIZ), the narrow strip between open ocean and the ice pack where the seasonal retreat of the main ice pack takes place. It is a highly variable sea ice environment, usually comprised of many individual floes of variable shape and size and made of mixed ice types, from young forming ice to fragmented multiyear ice. The presence of sea ice significantly affects the transport of energy and momentum between the atmosphere and ocean. Deformation of sea ice absorbs atmospheric surface stress acting on the ocean surface and resulting surface features affect aerodynamic drag. Ice cover prevents the local formation of surface gravity waves and attenuates and scatters waves that propagate from the open ocean. As a result, wave motions and wave-driven flows, such as Langmuir circulations, are greatly diminished below pack ice. The albedo of sea ice is large compared to open water, and most of the incoming solar radiation incident on sea ice is reflected back to the atmosphere. The thermal conductivity of sea ice is small, so sensible energy transport between ocean and atmosphere is limited in the presence of sea ice. Specialized Autonomous Ocean Flux Buoys have been developed to study wave effects, thermodynamic responses and turbulent coupling across the coupled ocean – ice – atmosphere system in the context of the larger MIZ DRI program.Award#: N0001412WX20737 , N0001412WX2112

Coupling of Waves, Turbulence and Thermodynamics Across the Marginal Ice Zone

LONG-TERM GOALS: Detailed process studies of the MIZ are necessary to build accurate Arctic region ice-ocean-atmosphere numerical models. Streove et al. (2007) provide an example of the challenges of modeling the Arctic ice-ocean-atmosphere system - current global circulation models under predict the observed trend of declining sea ice area over the last decade. A potential explanation for this under-prediction is that models are missing important feedbacks within the ocean-ice system, particularly in late summer low ice concentration conditions. Results from the proposed research will contribute to improving the upper ocean and sea ice physics contained in regional and global circulation models.Award Numbers: N0001415WX01195 and N0001415WX0187

Spectral Wave Decay Due to Bottom Friction on the Inner Shelf

LONG-TERM GOALS: Long term goals are to observe and model wave and current boundary layer processes to determine to wave dissipation and wave-bed interactions in coastal and nearshore regions using novel instrumentation techniques.Award#: N0001499WR3001

Near Shore Wave Processes

LONG-TERM GOALS: Long-term goals are to predict the wave-induced three-dimensional velocity field and induced sediment transport over arbitrary bathymetry in the near shore given the offshore wave conditions.Award #s: N0001499WR30116||N0001499WR30098||N0001499WR30146||N0001499WR30147Award #’s: N0001402WR20188, N0001402WR20376, N0001402WR2015

Leads Experiment (LEADEX) 1991, 1992

The Ocean Turbulence Laboratory in the Oceanography Department at the Naval Postgraduate School has an active research program addressing a range of ocean turbulent boundary layer problems. The group has developed observational systems for studying sub-ice boundary layers in polar regions, coastal internal waves, solitons and turbulence over the continental shelf, and the wave forced boundary bottom boundary layer over the inner shelf and surf zone.The ONR sponsored Leads Experiment provided an opportunity to measure timeseries of microstructure properties in the oceanic boundary layer under freezing leads during field programs in the Arctic Ocean north of Alaska in 1991 and 1992. Measurements were made for several days at downcurrent sides of newly formed leads by deploying huts and instrumentation within helicopter range of a central camp. At each lead the automated Loose Tethered Microstructure Profiler (LMP) continuously profiled the water column from the surface to 75m depth, spanning the 35m deep mixed layer and upper pycnocline. The LMP is equipped with a microscale shear probe, fast fp07 thermistor, and a microconductivity cell, providing centimeter resolution estimates of salinity and temperature structure while resolving the thermal and turbulent kinetic energy gradient spectrum to produce estimates of thermal dissipation rates, and kinetic energy dissipation rates. These estimates have been successfully used with very high resolution thermal gradients to estimate heat fluxes and thermal diffusivities within both the mixed layer and pycnocline

Manganese Oxide Thin Films Prepared by Nonaqueous Sol-Gel Processing: Preferential Formation of Birnessite

High quality manganese oxide thin films with smooth surfaces and even thicknesses have been prepared with a nonaqueous sol–gel process involving reduction of tetraethylammonium permanganate in methanol. Spin-coated films have been cast onto soft glass, quartz, and Ni foil substrates, with two coats being applied for optimum crystallization. The addition of alkali metal cations as dopants results in exclusive formation of the layered birnessite phase. By contrast, analogous reactions in bulk sol–gel reactions yield birnessite, tunneled, and spinel phases depending on the dopant cation. XRD patterns confirm the formation of well-crystallized birnessite. SEM images of Li-, Na-, and K–birnessite reveal extremely smooth films having uniform thickness of less than 0.5 μm. Thin films of Rb– and Cs–birnessite have more fractured and uneven surfaces as a result of some precipitation during the sol–gel transformation. All films consist of densely packed particles of about 0.1 μm. When tetrabutylammonium permanganate is used instead of tetraethylammonium permanganate, the sol–gel reaction yields amorphous manganese oxide as the result of diluted Mn sites in the xerogel film. Bilayer films have been prepared by casting an overcoat of K–birnessite onto an Na–birnessite film. However, Auger depth profiling indicates considerable mixing between the adjacent layers

Sound scattering by several zooplankton groups. II. Scattering models

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 236-253, doi:10.1121/1.421110.Mathematical scattering models are derived and compared with data from zooplankton from several gross anatomical groups—fluidlike, elastic shelled, and gas bearing. The models are based upon the acoustically inferred boundary conditions determined from laboratory backscattering data presented in part I of this series [Stanton et al., J. Acoust. Soc. Am. 103, 225–235 (1998)]. The models use a combination of ray theory, modal-series solution, and distorted wave Born approximation (DWBA). The formulations, which are inherently approximate, are designed to include only the dominant scattering mechanisms as determined from the experiments. The models for the fluidlike animals (euphausiids in this case) ranged from the simplest case involving two rays, which could qualitatively describe the structure of target strength versus frequency for single pings, to the most complex case involving a rough inhomogeneous asymmetrically tapered bent cylinder using the DWBA-based formulation which could predict echo levels over all angles of incidence (including the difficult region of end-on incidence). The model for the elastic shelled body (gastropods in this case) involved development of an analytical model which takes into account irregularities and discontinuities of the shell. The model for gas-bearing animals (siphonophores) is a hybrid model which is composed of the summation of the exact solution to the gas sphere and the approximate DWBA-based formulation for arbitrarily shaped fluidlike bodies. There is also a simplified ray-based model for the siphonophore. The models are applied to data involving single pings, ping-to-ping variability, and echoes averaged over many pings. There is reasonable qualitative agreement between the predictions and single ping data, and reasonable quantitative agreement between the predictions and variability and averages of echo data.This work was supported by the National Science Foundation Grant No. OCE-9201264, the U.S. Office of Naval Research Grant Nos. N00014-89-J-1729, N00014-95-1-0287, and N00014-94-1-0452, and the MIT/WHOI Joint Graduate Education Program

Acoustic diffraction by deformed edges of finite length : theory and experiment

Author Posting. © Acoustical Society of America, 2007. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 122 (2007): 3167-3176, doi:10.1121/1.2405126.The acoustic diffraction by deformed edges of finite length is described analytically and in the frequency domain through use of an approximate line-integral formulation. The formulation is based on the diffraction per unit length of an infinitely long straight edge, which inherently limits the accuracy of the approach. The line integral is written in terms of the diffraction by a generalized edge, in that the “edge” can be a single edge or multiple closely spaced edges. Predictions based on an exact solution to the impenetrable infinite knife edge are used to estimate diffraction by the edge of a thin disk and compared with calculations based on the T-matrix approach. Predictions are then made for the more complex geometry involving an impenetrable thick disk. These latter predictions are based on an approximate formula for double-edge diffraction [Chu et al., J. Acoust. Soc. Am. 122, 3177 (2007)] and are compared with laboratory data involving individual elastic (aluminum) disks spanning a range of diameters and submerged in water. The results of this study show this approximate line-integral approach to be versatile and applicable over a range of conditions.This research was supported by the U.S. Office of Naval Research (Grant No. N00014-02-0095), WHOI, and by a grant of computer time at the U.S. Department of Defense High Performance Computing Shared Resource Center (Naval Research Laboratory, Washington, DC)

Sound scattering by several zooplankton groups. I. Experimental determination of dominant scattering mechanisms

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 225-235, doi:10.1121/1.421469.The acoustic scattering properties of live individual zooplankton from several gross anatomical groups have been investigated. The groups involve (1) euphausiids (Meganyctiphanes norvegica) whose bodies behave acoustically as a fluid material, (2) gastropods (Limacina retroversa) whose bodies include a hard elastic shell, and (3) siphonophores (Agalma okeni or elegans and Nanomia cara) whose bodies contain a gas inclusion (pneumatophore). The animals were collected from ocean waters off New England (Slope Water, Georges Bank, and the Gulf of Maine). The scattering properties were measured over parts or all of the frequency range 50 kHz to 1 MHz in a laboratory-style pulse-echo setup in a large tank at sea using live fresh specimens. Individual echoes as well as averages and ping-to-ping fluctuations of repeated echoes were studied. The material type of each group is shown to strongly affect both the overall echo level and pattern of the target strength versus frequency plots. In this first article of a two-part series, the dominant scattering mechanisms of the three animal types are determined principally by examining the structure of both the frequency spectra of individual broadband echoes and the compressed pulse (time series) output. Other information is also used involving the effect on overall levels due to (1) animal orientation and (2) tissue in animals having a gas inclusion (siphonophores). The results of this first paper show that (1) the euphausiids behave as weakly scattering fluid bodies and there are major contributions from at least two parts of the body to the echo (the number of contributions depends upon angle of orientation and shape), (2) the gastropods produce echoes from the front interface and possibly from a slow-traveling circumferential (Lamb) wave, and (3) the gas inclusion of the siphonophore dominates the echoes, but the tissue plays a role in the scattering and is especially important when analyzing echoes from individual animals on a ping-by-ping basis. The results of this paper serve as the basis for the development of acoustic scattering models in the companion paper [Stanton et al., J. Acoust. Soc. Am. 103, 236–253 (1998)].This work was supported by the National Science Foundation Grant No. OCE- 9201264, the U.S. Office of Naval Research Grant Nos. N00014-89-J-1729 and N00014-95-1-0287, and the MIT/ WHOI Joint Graduate Education Program

Ice Scallops: A Laboratory Investigation of the Ice-Water Interface

The article of record as published may be found at https://doi.org/10.1017/jfm.2019.398Ice scallops are a small-scale (5–20cm) quasi-periodic ripple pattern that occurs at the ice-water interface. Previous work has suggested that scallops form due to a self-reinforcing interaction between an evolving ice-surface geometry, an adjacent turbulent flow field, and the resulting differential melt rates that occur along the interface. In this study, we perform a series of laboratory experiments in a refrigerated flume to quantitatively investigate the mechanisms of scallop formation and evolution in high resolution. Using particle-image velocimetry, we probe an evolving ice-water boundary layer at sub-millimeter scales and 15Hz frequency. Our data reveals three distinct regimes of ice-water interface evolution: A transition from flat to scalloped ice; an equilibrium scallop geometry; and an adjusting scallop interface. We find that scalloped ice geometry produces a clear modification to the ice-water boundary layer, characterized by a time- mean recirculating eddy feature that forms in the scallop trough. Our primary finding is that scallops form due to a self reinforcing feedback between the ice-interface geometry and shear production of turbulent kinetic energy in the flow interior. The length of this shear production zone is therefore hypothesized to set the scallop wavelength