The aim of this work is to shed light by revisiting - through the kernel-wave
(KW) perspective - the breakdown of a quasi-geostrophic (QG) mixing layer (or
vortex strip/filament) in atmosphere under the influence of a background shear.
The QG mixing layer is modelled with a family of quasi-Rayleigh velocity
profiles in which the potential vorticity (PV) is constant in patches. In the
KW perspective a counter-propagating Rossby wave (CRW) is created at each PV
edge, i.e. the edge where a PV jump is located. The important parameters of our
study are (i) the vorticity of the uniform shear m and (ii) the Rossby
deformation radius Ld, which indicates how far the pressure perturbations can
vertically propagate. While an adverse shear (m < 0) stabilizes the system, a
favorable shear (m > 0) strengthens the instability. This is due to how the
background shear affects the two uncoupled CRWs by shifting the optimal phase
difference towards large (small) wavenumber when m 0). As the QG
environment is introduced a general weakening of the instability is noticed,
particularly for m > 0..
