A new look at shear instability in density-stratified geophysical flows
Jan-Bert Flor (EReS)
The traditional approach to assessing shear-driven instability and
mixing in density-stratified geophysical flows is to appeal to the
Kelvin-Helmholtz mode of instability. This involves the generation of
turbulence and mixing when the destabilizing shear overwhelms the
stabilizing influence of the density stratification, and is a common
conceptual basis for turbulence and mixing parameterizations.
However, this is a simplified view that does not consider alternate
modes of instability and mixing in which the density stratification
acts as a destabilizing influence on the flow. One such mode - the
Holmboe mode - leads to the generation of internal waves that may
cause turbulence and mixing through a fundamentally different process.
The unique mixing behaviour, evolution of the wave field, and
identification of Holmboe waves in a highly-stratified estuary are all
described through the combined use of numerical simulations,
laboratory experiments, field observations and analytical methods.