Instability of coastal currents

We have been studying the stability of shallow, density-driven boundary currents. Basic flow shown below has a depth of 20 m, maximal along-shore velocity = 0.3 m/s, M² ~ 1.5e-6 (1/s²), N² ~ 0.0015 (1/s²). Its geometry is similar to that of river-fed coastal currents like Adriatic Coastal Current, China Coastal Current, Soya warm current, etc.

It can be seen that the flow becomes baroclinically unstable, with alternating onshore/offshore flows, in a few days. Our goal is to understand the factors that influence the growth rate, length and velocity scales.

 

The instabilities (largely baroclinic) seen above are influenced by a number of processes, including non-geostrophic basic flow (i.e. balanced Richardson number Ri of O(1)), bottom drag, bottom slope, etc. The complexity had led us to consider the individual effects, which are described in a paper:

Chen, S. N., C. J. Chen, and J. A. Lerczak, 2020: On baroclinic instability over continental shelves: Testing the utility of Eady-type models. Journal of
Physical Oceanography, 50, 3-33.


Some of the results can be found in a poster presented at the Gordon Research Conference in 2019.