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• 1. [Article] Asymmetry of Tidal Plume Fronts in an Eastern Boundary Current Regime

  The Columbia River tidal plume or near-field is formed twice daily by the ebb outflow of the Columbia River. It is a part of a larger, anticyclonic plume bulge, which in turn is embedded in far-field plume ...

  Citation × Citation Citation Abstract Copy Title: Asymmetry of Tidal Plume Fronts in an Eastern Boundary Current Regime Author: Jay, David A., Pan, Jiayi, Orton, Philip M., Horner-Devine, Alexander R. Year: 2006 The Columbia River tidal plume or near-field is formed twice daily by the ebb outflow of the Columbia River. It is a part of a larger, anticyclonic plume bulge, which in turn is embedded in far-field plume and coastal waters. Because of the mixing caused directly and indirectly by plume fronts, the interaction of the tidal plume and bulge with the California Current upwelling regime plays a vital role in coastal productivity on the Oregon and Washington shelves. The tidal plume is initially supercritical with respect to the internal Froude number on all stronger ebbs. It is separated from the plume bulge by a front, whose properties are very different under upwelling vs. downwelling conditions. Under summer upwelling conditions, this front is sharp and narrow (only 50-100 m wide on its upwind or northern side) and marks a transition from supercritical to subcritical flow for 6-12 hours after high water. This sharp front is a source of turbulent mixing, despite the strong stratification. Because the tidal plume may overlie newly upwelled waters, these fronts can mix nutrients into the plume, enhancing primary productivity. Symmetry would suggest that there should be a sharp front south of the estuary mouth under summer downwelling conditions. Instead, the downwelling tidal plume front is usually broad (up to several km) and diffuse on the upstream side. Less mixing occurs, and the water immediately below the plume consists of old plume and surface ocean waters, both low in nutrients. There is also a second up-welling-downwelling asymmetry. Supercritical upwelling plume fronts often generate solitons trains as they slow and transition to a subcritical state. These soliton trains contribute to vertical mixing in the plume bulge and have a non-zero Stokes drift so that they transport low-salinity water across the tidal plume into the plume bulge. Under downwelling conditions, soliton forma-tion is uncommon. Moreover, solition formation almost always begins on the south side of the plume so that the front "unzips" from south to north. This implies that a frontal transition from supercritical to subcritical conditions first occurs on the south side tidal plume, regardless of whether this is the upwind or downwind side of the plume. This contribution describes and analyzes these two asymmetries using vessel data, SAR images and a vorticity analysis. Internal Froude number and plume depth are key parameters in distinguishing the upwelling and downwelling situations, and the observed asymmetries can be explained in terms of potential vorticity conservation. The tidal outflow embeds relative vorticity in the emerging tidal plume water mass. This vorticity controls the transition of the tidal plume front to a subcritical state and the timing and location of internal wave generation by plume fronts. Title: Asymmetry of Tidal Plume Fronts in an Eastern Boundary Current Regime Author: Jay, David A., Pan, Jiayi, Orton, Philip M., Horner-Devine, Alexander R. Year: 2006 The Columbia River tidal plume or near-field is formed twice daily by the ebb outflow of the Columbia River. It is a part of a larger, anticyclonic plume bulge, which in turn is embedded in far-field plume and coastal waters. Because of the mixing caused directly and indirectly by plume fronts, the interaction of the tidal plume and bulge with the California Current upwelling regime plays a vital role in coastal productivity on the Oregon and Washington shelves. The tidal plume is initially supercritical with respect to the internal Froude number on all stronger ebbs. It is separated from the plume bulge by a front, whose properties are very different under upwelling vs. downwelling conditions. Under summer upwelling conditions, this front is sharp and narrow (only 50-100 m wide on its upwind or northern side) and marks a transition from supercritical to subcritical flow for 6-12 hours after high water. This sharp front is a source of turbulent mixing, despite the strong stratification. Because the tidal plume may overlie newly upwelled waters, these fronts can mix nutrients into the plume, enhancing primary productivity. Symmetry would suggest that there should be a sharp front south of the estuary mouth under summer downwelling conditions. Instead, the downwelling tidal plume front is usually broad (up to several km) and diffuse on the upstream side. Less mixing occurs, and the water immediately below the plume consists of old plume and surface ocean waters, both low in nutrients. There is also a second up-welling-downwelling asymmetry. Supercritical upwelling plume fronts often generate solitons trains as they slow and transition to a subcritical state. These soliton trains contribute to vertical mixing in the plume bulge and have a non-zero Stokes drift so that they transport low-salinity water across the tidal plume into the plume bulge. Under downwelling conditions, soliton forma-tion is uncommon. Moreover, solition formation almost always begins on the south side of the plume so that the front "unzips" from south to north. This implies that a frontal transition from supercritical to subcritical conditions first occurs on the south side tidal plume, regardless of whether this is the upwind or downwind side of the plume. This contribution describes and analyzes these two asymmetries using vessel data, SAR images and a vorticity analysis. Internal Froude number and plume depth are key parameters in distinguishing the upwelling and downwelling situations, and the observed asymmetries can be explained in terms of potential vorticity conservation. The tidal outflow embeds relative vorticity in the emerging tidal plume water mass. This vorticity controls the transition of the tidal plume front to a subcritical state and the timing and location of internal wave generation by plume fronts. Close

• 2. [Article] Observations at the Tidal Plume Front of a High-Volume River Outflow

  We present shipboard observations of very strong convergence, vertical velocities and mixing, and near-bed impacts associated with the leading-edge front of the tidally-pulsed Columbia River plume. With ...

  Citation × Citation Citation Abstract Copy Title: Observations at the Tidal Plume Front of a High-Volume River Outflow Author: Orton, Philip M., Jay, David A. Year: 2005 We present shipboard observations of very strong convergence, vertical velocities and mixing, and near-bed impacts associated with the leading-edge front of the tidally-pulsed Columbia River plume. With upwelling-favorable winds and riverflow of 4900 m3s−1, the plume propagates as a buoyant gravity current with a rotary, bore-like vertical frontal circulation and downwelling as strong as 0.35 m s−1. In waters as deep as 65 m, near-bed currents intensify to as much as 1.0 m s−1 after frontal passage, and are often associated with elevated acoustic backscatter. Mixing is locally strong, with an eddy diffusivity of O(0.2 m2s−1) 50 m behind the front, and T-S diagrams imply plume mixing with 10 m deep ocean water. These observations indicate that the leading-edge front of a surface-advected plume can cause exchanges of (a) nutrients between cold subsurface shelf waters and the river plume, and (b) nutrients and sediments across the sediment-water interface. Title: Observations at the Tidal Plume Front of a High-Volume River Outflow Author: Orton, Philip M., Jay, David A. Year: 2005 We present shipboard observations of very strong convergence, vertical velocities and mixing, and near-bed impacts associated with the leading-edge front of the tidally-pulsed Columbia River plume. With upwelling-favorable winds and riverflow of 4900 m3s−1, the plume propagates as a buoyant gravity current with a rotary, bore-like vertical frontal circulation and downwelling as strong as 0.35 m s−1. In waters as deep as 65 m, near-bed currents intensify to as much as 1.0 m s−1 after frontal passage, and are often associated with elevated acoustic backscatter. Mixing is locally strong, with an eddy diffusivity of O(0.2 m2s−1) 50 m behind the front, and T-S diagrams imply plume mixing with 10 m deep ocean water. These observations indicate that the leading-edge front of a surface-advected plume can cause exchanges of (a) nutrients between cold subsurface shelf waters and the river plume, and (b) nutrients and sediments across the sediment-water interface. Close

• 3. [Article] A Multi-Class Suspended Particulate Matter Calibration for Bottom Boundary Layers

  We present a multi-class suspended particulate matter (SPM) calibration for use with in situ water sample SPM concentration data and backscatter (or transmission) from one or more acoustic and optical ...

  Citation × Citation Citation Abstract Copy Title: A Multi-Class Suspended Particulate Matter Calibration for Bottom Boundary Layers Author: Orton, Philip M., Jay, David A., Wilson, D. J. Year: 2003 We present a multi-class suspended particulate matter (SPM) calibration for use with in situ water sample SPM concentration data and backscatter (or transmission) from one or more acoustic and optical sensors. The output of this calibration is high-resolution SPM concentration data in several discrete settling velocity (Ws) classes. Separately for each sensor, the calibration involves three steps: (1) a calibration of backscatter to total SPM concentration; (2) a decomposition of resulting concentration data into several Wsclasses, utilizing a dynamical vertical SPM profile model; and (3) a sensor bias calibration where water sample concentration data are used to correct for the sediment size-dependence of sensor response. Multiple sensors can be incorporated to improve the results, as step 3 can objectively choose the best sensor for monitoring each Ws-class. The calibration is generally applicable in wave-current boundary layers, though this paper is focused on currents only. We demonstrate the method using data from greater-ebb SPM export events in the Fraser River estuary, when salt has washed out beyond the river entrance, surface currents are strong (3+ m s??) and turbulent mixing is intense. The resulting concentration estimates show good agreement with in situ particle-size observations near the bed, but discrepancies increasing with height above the bed, likely due to violation of model assumptions in the outer part of the water column. An uncertainty analysis indicates that the standard deviation in concentration estimates is 32-48%, primarily due to poor near-bed acoustic data coverage and uncertainty in water sample concentration data. We conclude by discussing planned improvements for strongly advective and aggregate-dominated systems. Title: A Multi-Class Suspended Particulate Matter Calibration for Bottom Boundary Layers Author: Orton, Philip M., Jay, David A., Wilson, D. J. Year: 2003 We present a multi-class suspended particulate matter (SPM) calibration for use with in situ water sample SPM concentration data and backscatter (or transmission) from one or more acoustic and optical sensors. The output of this calibration is high-resolution SPM concentration data in several discrete settling velocity (Ws) classes. Separately for each sensor, the calibration involves three steps: (1) a calibration of backscatter to total SPM concentration; (2) a decomposition of resulting concentration data into several Wsclasses, utilizing a dynamical vertical SPM profile model; and (3) a sensor bias calibration where water sample concentration data are used to correct for the sediment size-dependence of sensor response. Multiple sensors can be incorporated to improve the results, as step 3 can objectively choose the best sensor for monitoring each Ws-class. The calibration is generally applicable in wave-current boundary layers, though this paper is focused on currents only. We demonstrate the method using data from greater-ebb SPM export events in the Fraser River estuary, when salt has washed out beyond the river entrance, surface currents are strong (3+ m s??) and turbulent mixing is intense. The resulting concentration estimates show good agreement with in situ particle-size observations near the bed, but discrepancies increasing with height above the bed, likely due to violation of model assumptions in the outer part of the water column. An uncertainty analysis indicates that the standard deviation in concentration estimates is 32-48%, primarily due to poor near-bed acoustic data coverage and uncertainty in water sample concentration data. We conclude by discussing planned improvements for strongly advective and aggregate-dominated systems. Close