Mean-flow in lower canyon about internal_waves_barkley_canyon HOT 6 CLOSED

@jklymak

See above comment for a start on the up-canyon mean flow at Axis.

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Can you zoom in on one or two regions time. It really seems there is a sense of propagation to these....

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@jklymak

• Plot 1 shows Jan-Mar and Plot 2 shows Jun-Aug.
• There appears to some upward propagation of the positive velocities.
• Some appear to form at the bottom and strengthen as they move upward.
• There looks to be periodicity of about a week, and/or less.
• Question: Why do they strengthen away from the bottom? Some sort of shear effect?
• Question: Why is the apparent periodicity a few days to a week? This seems to be odd timing.
• Hotchiss and Wunsch (1982) found evidence of upward propagation in internal wave driven near-bottom up-canyon mean flows (Hudson Canyon). They claim the flows must develop upward propagation as they move up the canyon, to account for the bottom slope. They also mention these flows being partially driven by long-term large-scale quasi-geostrophic flows along the canyon mouth that have periods of > a few days.
• Petruncio et al. (1998) found evidence of shoreward progressive internal wave driven flows with energy shoaling towards shore at an angle similar to the angle of the canyon floor, though these were generally of semidiurnal period.

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Hi Kurtis, Great job finding those references. I do wonder if this is an example of "tidal rectification" where the tidal flow is non-linear, and there is a low-frequency component that comes from the modification of the "triangle" wave of the flow. If it is just tidal rectification, though, the total transport (top to bottom, side to side) should be zero. Even if you include the deep data, does this get driven to (almost) zero total transport?

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@jklymak

• As a rough estimate of total transport (along-canyon), if I extend the range (between dashed lines) for the annual mean velocity to include the deep data (650 m - bottom) the values for each year are approximately halved (0.004 - 0.005 m/s).
• From one of Garrett's lectures on tidal rectification, in an observational situation with friction, etc. on a sloping bottom, the tidal rectification should result in an upper flow that follows a pressure gradient up-slope (in our case, up-canyon), with reversed flow near the bottom - if the U forcing is great enough. The net-flow would be slightly up-slope, even including the deep data, unless I misunderstand. It was only a brief lecture and didn't get into any triangle waves, net-zero transport, etc.

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• Try to find a connection for the odd periodicity.
• Spring-neap comparison?
• Semidiurnal band forcing?
• Slope low-pass currents?

• From the rough qualitative comparison, below, there are no obvious similarities in periodicity that may indicate forcing. Shown is a two month period with the depth-mean along-canyon low-pass velocities (black), surface spring-neap levels (blue), along-slope depth-mean low-pass velocities (orange), and along-canyon depth-mean semidiurnal power (green).
  
• Zoomed out to 6-month and annual periods there is still no obvious relationship.
  
• Finish write-up and plots in thesis.

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