Dynamics of rotor formation in uniformly stratified two-dimensional flow over a mountain

In contrast, in near-hydrostatic flows boundary-layer rotors form even if the wave amplitude predicted by linear theory is relatively small. In such cases, rotors appear to be decoupled from the wave field aloft by low-level wave breaking. In fact, rotor formation is caused by short-wavelength modes propagating horizontally along an elevated and stably stratified jet below the neutrally stratified wave-breaking region.

Once formed, atmospheric rotors trigger non-hydrostatic wave modes that can penetrate through the finite-depth neutral layer above the jet and propagate into the free atmosphere. In all simulated cases, non-hydrostatic effects—i.e. sharp vertical accelerations—appear to be essential for rotor formation, regardless of the degree of hydrostaticity in the primary wave field.