Sub-diurnal summary

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• [x] Outline this summary, for reference.

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• Bandwidth 2e-6 Hz to 1e-5 Hz (first non-zero frequency bin to < diurnal peak).
• Notable effects: Near-shelf intensification. Canyon-axis intensification. Seasonality.

Subdiurnal outline

Upper Slope - Near-shelf intensification

Describe (what do I see):

• Depth-averaged / multi-annual time-averaged PSD comparison to K1, f, and M2. About K1/f equivalent at the lower end, diminishes by an order of magnitude before reaching the K1 peak.
• Most of depth equally distributed between cross- and along-slope, and nearly rectilinear in CW and CCW, with slightly more power in the cross-slope and CW components.
• Below -250 m intensification in along-slope, CCW signal, of about 2x orders of magnitude, to overtake cross-slope / CW signal in the lower depths.
• Vertical scale of effect approximately 150 m AB.
• Seasonality evident in prominent events in the fall and winter, with a spring/summer lull.
• Spring-neap is not obvious, but may be evident in barotropic time series (compare local vs remote forcing).
• Be sure these are all quantified and related in clear figures.

Compare (what did others see):

• Allen, 1976.
• Thomson & Crawford, 1982.
• Chapman, 1983.
• Crawford & Thomson, 1984.
• Crawford, 1984.
• Hotchkiss & Wunsch (1982) found evidence of up to a 10x increase along-slope near to Hudson Canyon, and a vertical scale for the effect of about 150 m AB around -400 m depth. Correlation to direction and strength of both prevailing winds and mean currents, and storm events.
• Flather, 1988.
• Brink, 1991.
• Drakopoulos & Marsden, 1993.
• Foreman & Thomson, 1997.
• Polzin et al. (1997) found an increase of about 15x up to about 150 m over slope topography.
• Cummins et al., 2001.
• Jayne & St. Laurent, 2001.
• Nash et al. (2004) found similar effects at the Mid-Atlantic Bight slope off of Virginia.
• Kelly et al., 2010.
• Klymak et al., 2011.
• Klymak et al., 2012.
• Kunze et al. (2012) found similar effects at the slope near Monterey and Soquel canyons.
• Klymak et al., 2013.
• Martini et al., 2013.
• Johnston & Rudnick, 2014.
• Terker et al., 2014.
• Gemmrich & Klymak, 2015.
• Robertson et al., 2017.
• Quantify (compare) where possible.
• Find additional sources.

Explain (what may be causing this):

• Evanescent (subdiurnal is sub-inertial) internal waves locally generated from 'rubbing' subdiurnal currents incident with the subcritical upper-slope (radiate upwards) (Hotchiss & Wunsch, Polzin, Kunze, Cummins).
• Increased stratification effects near areas of high 'topographic relief', such as the shelf-break and slopes. These highly stratified turbulent layers experience the effects of reflection/scattering and internal tide and lee-wave generation. May amplify internal waves, in general.
• Discuss strengths and weaknesses of each theory.

Axis - Canyon-axis intensification

Describe (what do I see):

• Depth-averaged / multi-annual time-averaged PSD comparison to K1, f, and M2. Less than K1 or f throughout the band, and relatively level.
• Most of depth along-canyon, and rectilinear in CW and CCW.
• Below -750 m intensification in along-canyon, rectilinear signal, of about 2x orders of magnitude.
• Vertical scale of effect approximately 250 m AB.
• Seasonality is less evident in the canyon, but select prominent events in the fall and winter may still be visible.
• Spring-neap is not obvious, but may be evident in barotropic time series (compare local vs remote forcing).
• Be sure these are all quantified and related in clear figures.

Compare (what did others see):

• Hotchkiss & Wunsch (1982) also found evidence of increased internal tides within Hudson Canyon, with a vertical scale for the effect of about 250 m AB around -800 m depth. Correlation to direction and strength of both prevailing winds and mean currents, as they affect upwelling which drives along-canyon currents. Only very strong storm events evident.
• Petruncio et al., 1998.
• Carter & Gregg (2002) observed a 200-300 m thick intensified bottom layer along the axis of Monterey Canyon.
• Xu & Noble, 2009.
• Kunze et al. (2002, 2012) found similar effects within both Monterey Canyon and Soquel Canyon, with intensification of over an order of magnitude at a vertical scale approximate 200 - 300 m AB near to -1000 m depth.
• Wain et al., 2013.
• Alberty et al., 2017.
• Kampf, 2018.
• Hamann & Alford, 2020.
• Quantify (compare) where possible.
• Find additional sources.

Explain (what may be causing this):

• Evanescent (subdiurnal is sub-inertial) internal waves locally generated from 'rubbing' subdiurnal currents incident with the irregular canyon topography (floor/slope and wall features).
• Topographically increased stratification (as for Upper Slope) amplifying the local internal waves.
• Discuss strengths and weaknesses of each theory.

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Closed, for reference. Adapted into new 'chapters'.