Short-Period Variations in a Great Lakes Coastal Current by Aerial Photogrammetry

Yeske, Lanny A.; Green, Theodore

doi:10.1175/1520-0485(1975)005<0125:spviag>2.0.co;2

Cited by 7 publications

(5 citation statements)

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“…A primary focus of KITES is a seasonal coastal flow known as the Keweenaw Current. Flowing northeastward along the western shoreline of Lake Superior's Keweenaw Peninsula (Figure 1), this current tends to intensify downstream and can reach speeds on the order of 1 m s −1 near the tip of the peninsula [ Yeske and Green , 1975; Niebauer et al , 1977; Green and Terrell , 1978; H. J. Niebauer and E. A. Ralph, Episodic events in the Keweenaw Current in Lake Superior: A retrospective, submitted to Journal of Geophysical Research , 2004, hereinafter referred to as Niebauer and Ralph, submitted manuscript, 2004]. A numerical modeling investigation by Chen et al [2001] and Zhu et al [2001] has indicated that the Keweenaw Current is partly a thermally driven flow, caused by rapid warming of nearshore (versus offshore) water.…”

Section: Settingmentioning

confidence: 99%

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

2004

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[1] Data from near-bottom instruments reveal that the mechanisms responsible for generating bottom stresses and resuspending sediment over the shelf and slope off of Lake Superior's Keweenaw peninsula exhibit distinct seasonal variations. Notably, near-bottom flows over the slope are persistently weak (<10 cm s À1 ) during summer but frequently attain high speeds, in excess of 20 cm s À1 , in autumn and winter. During the intense storms of autumn and winter the generation of bottom stress is enhanced by the action of near-bottom orbital velocities due to surface waves. Even at 90-m depth, orbital velocities can increase bottom stress by a factor of up to 20% during storms. Where the seasonal thermocline intersects the lake floor, bottom stress is also considerably enhanced, often by more than a factor of 2, by high-frequency motions in the internal wave band. Over the Keweenaw slope, sediment resuspension is largely confined to autumn and winter episodes of high bottom stress. Our analysis indicates that this resuspended material tends to be carried offshore, a phenomenon that is partly due to the coincidence of the direction of the buoyancy-driven component of the Keweenaw Current with downwelling favorable alongshore winds. As a result of this coincidence, currents and bottom stresses tend to be greater during periods of downwelling, as opposed to upwelling, circulation. A potential challenge to modeling storm-driven resuspension in the study region is indicated by observations that the minimum stress required for resuspension may vary significantly with time over the autumn and winter.

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Section: Settingmentioning

confidence: 99%

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

2004

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“…Several observational studies have been conducted to characterize the features of the Keweenaw Current and its relation to the thermal bar and winds Green and Yeske 1974;Ragotzkie 1974;Yeske and Green 1975;Diehl et al 1977;Niebauer et al 1977;Bennett 1978). Based on hydrographic, wind, and current measurements taken on a transect near Eagle Harbor in July 1973, Niebauer et al (1977 first comprehensively described the wind-and buoyancy-driven nature of the Keweenaw Current.…”

Section: Introductionmentioning

confidence: 99%

Prognostic Modeling Studies of the Keweenaw Current in Lake Superior. Part II: Simulation

et al. 2001

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The formation and evolution of the Keweenaw Current in Lake Superior were examined using a nonorthogonalcoordinate primitive equation numerical model. The model was initialized by the monthly averaged temperature field observed in June and September 1973 and run prognostically under different forcing conditions with and without winds. As a Rossby adjustment problem, the model predicted the formation of a well-defined coastal current jet within an inertial period of 16.4 h after the current field adjusted to the initial temperature field. The magnitude and direction of this current jet varied with the cross-shelf temperature gradient and wind velocity. It tended to intensify during northeastward (downwelling favorable) winds, and to lessen, or even reverse, during southwestward to northwestward (upwelling favorable) or southeastward (downwelling favorable) winds. In a case with strong stratification and without external atmospheric forcings, a well-defined clockwise warm-core eddy formed near the northeastern coast of the Keweenaw Peninsula as a result of baroclinic instability. A warmcore eddy was detected recently from satellite surface temperature images, the shape and location of which were very similar to those of the model-predicted eddy. The energy budget analysis suggested that the eddy kinetic energy grew exponentially over a timescale of 7 days. Growth was due to a rapid energy transfer from available eddy potential energy. The subsequent decline of the eddy kinetic energy was the result of turbulent diffusion, transfer from the eddy kinetic energy to mean kinetic energy, and outward net energy flux.

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“…Historically, drift cards, or computer punch cards, and bottles have been used to study surface Lagrangian transport for well over a century (Garstang, 1898). In the past, drift cards typically provided only information about initial and final locations (e.g., Williams et al, 1977;Levin, 1983), though in rare cases they have been used to quantify short-term transport (Yeske and Green, 1975).…”

Section: Design Requirementsmentioning

confidence: 99%

“…However, they have not been connected, conceptually or technologically, to the larger scales observed by surface drifters. To fill this observational gap, the classic tools of messages in bottles (e.g., Williams et al, 1977) and drift cards (e.g., Yeske and Green, 1975) were brought into the modern era: Continuous quantitative visual monitoring, as in the famous parsnip experiments of Richardson and Stommel (1948), of buoyant and biodegradable bamboo dinner plates from a ship-tethered aerostat equipped with a high-resolution camera and positioning system. Section 2.1 and Table 1 outline the minimum operating requirements for observations of Lagrangian transport at the air-sea interface in the open ocean that resolve the spatiotemporal scales relevant to oceanic boundary layer turbulence.…”

Section: Introductionmentioning

confidence: 99%

Surface Ocean Dispersion Observations From the Ship-Tethered Aerostat Remote Sensing System

et al. 2018

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Oil slicks and sheens reside at the air-sea interface, a region of the ocean that is notoriously difficult to measure. Little is known about the velocity field at the sea surface in general, making predictions of oil dispersal difficult. The Ship-Tethered Aerostat Remote Sensing System (STARSS) was developed to measure Lagrangian velocities at the air-sea interface by tracking the transport and dispersion of bamboo dinner plates in the field of view of a high-resolution aerial imaging system. The camera had a field of view of approximately 300 × 200 m and images were obtained every 15 s over periods of up to 3 h. A series of experiments were conducted in the northern Gulf of Mexico in January-February 2016. STARSS was equipped with a GPS and inertial navigation system (INS) that was used to directly georectify the aerial images. A relative rectification technique was developed that translates and rotates the plates to minimize their total movement from one frame to the next. Rectified plate positions were used to quantify scale-dependent dispersion by computing relative dispersion, relative diffusivity, and velocity structure functions. STARSS was part of a nested observational framework, which included deployments of large numbers of GPS-tracked surface drifters from two ships, in situ ocean measurements, X-band radar observations of surface currents, and synoptic maps of sea surface temperature from a manned aircraft. Here we describe the STARSS system and image analysis techniques, and present results from an experiment that was conducted on a density front that was approximately 130 km Carlson et al. Surface Ocean Dispersion Observations offshore. These observations are the first of their kind and the methodology presented here can be adopted into existing and planned oceanographic campaigns to improve our understanding of small-scale and high-frequency variability at the air-sea interface and to provide much-needed benchmarks for numerical simulations.

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Short-Period Variations in a Great Lakes Coastal Current by Aerial Photogrammetry

Cited by 7 publications

References 0 publications

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

Prognostic Modeling Studies of the Keweenaw Current in Lake Superior. Part II: Simulation

Surface Ocean Dispersion Observations From the Ship-Tethered Aerostat Remote Sensing System

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