evidence of strong shear in much of the data, and we are interested in
whether this shear is strong enough to initiate dynamical instabilities
leading to vertical mixing to lead to higher vertical heat (and salt and
nutrient) fluxes. We use the
Richardson number (Ri) calculated with ADCP and CTD data, as a proxy for mixing. It is basically a ratio of the Buoyancy
Frequency to Shear^2. Formally, Ri<1/4 is the criterion for dynamic shear
instability starting from an infinitesimal disturbance. Ri values of 1 or less indicate the
potential for instability (basically, wave-breaking) in a finite-amplitude
disturbance such as one might get from high-frequency internal gravity waves.
Because of ADCP resolution issues, any values less than 1 suggests that
turbulence might also be possible through dynamic shear instability occurring
on spatial scales smaller than the ADCP can resolve (~8 m).
|Next we’ll show
an example of applying this to one station.