Closed kurtisanstey closed 2 years ago
Summary update
Adjusted smoothed wind magnitude / direction plots to be more useful.
Performed CW rotary spectrograms on the vector wind data.
A band-pass integral on the rotary spectrograms produced CW and CCW near-inertial wind data for each year.
It is useful to simply look at the CW near-inertial wind component, as Alford (2001) states that it is this component that contributes most to the near-inertial internal wave field (though the CCW component does contribute some small amount).
The intensity of this contribution depends on the CW near-inertial winds, but also the depth of the mixed layer, leading to a significant (up to 12x) increase in near-inertial internal wave energy input, peaking in October and through the winter, and lowest in the summer (D'Asaro, 1985).
Thicker mixed-layer 'strums' low modes more.
Larger synoptic scale events do not excite much inertial energy; it is the smaller cold fronts or small lows that contribute most (~100 km).
For the slab model, steps were taken as outlined by Alford (2001).
First a time series of wind stress was determined as for D'Asaro (1985) using Garratt's (1977) canonical drag coefficient and the complex surface wind velocities.
Slab layer currents and input flux computed as in D'Asaro (1985) and Alford (2001).
[x] Look into seasonal mixed layer depth.
[x] Check if f peak is super-inertial for local vs remote forcing.
Line P station 3 seasonal mixed-layer depth as in Thomson and Fine (2003) and Li et al. (2004). The mixed-layer is thinnest mid-May through mid-November:
The addition of the seasonal mixed-layer depth dampens wind contributions to mixed-layer currents in the winter/spring.
The values for both mixed-layer currents (up to ~0.5 m/s) and flux (up to ~0.25 W/m^2) are similar to what was obtained by both D'Asaro (1985) and Alford (2001).
Looking at the near-inertial CW component of the mixed-layer currents as the main contributor to near-inertial internal waves, significant wind events during thin mixed-layer months line up well with what is seen making it into the canyon, suggesting local forcing:
Furthermore, in higher frequency resolution spectra, the f peak does not appear to be super-inertial, reinforcing evidence for local forcing. In previous PSD the slight shift towards higher frequencies could have been a result of over-averaging.
Observed:
Speculation:
Notes for write-up:
Gathering the pieces:
Slope:
Axis:
Some samples:
Vertical modes:
Mode amplitude seasonality, 2013:
Forcing comparison, 2013:
Saving this as analysis reference. New issue for writing the chapter.