Nonmodal development of baroclinic waves undergoing horizontal shear deformation

Abstract

The evoluation of waves in a basic state containing a constant vertical shear and a smaller constant horizontal shear is considered. The "PV-thinking" associated with counterprogating Rossby potential vorticity (PV) edge waves found at the horizontal boundaries is used to interpret the evolution of the waves. The presence of the barotropic shear introduces a time-dependent y wavenumber, which in turn, makes the total horizontal wavenumber a function of time. For properly configured initial (x, y) wavenumbers, the horizontal wavenumber decreases at first. This decrease induces an increase in the scale of the disturbances and a growth associated with downgradient momentum fluxes. The PV edge w..