Nonlinear Gravity Waves in the MLT: Self-Acceleration Dynamics and Instabilities (Invited)

Gravity wave (GW) packets penetrating to high altitudes exhibit dynamics referred to as 'self acceleration', in which the GW phase speed is accelerated in the direction of GW propagation due to transient convergent momentum fluxes accompanying GW packet localization. Because these effects are localized in the vertical, they distort the GW phase structure of the primary packet, ultimately causing the vertical group velocity to become zero and the packet to stall. Stalling is accompanied by two-dimensional (2D) instabilities for all GW scales, frequencies, and Reynolds numbers assessed to date. Three-dimensional (3D) instabilities nevertheless also occur, but they arise following initial 2D instabilities in all cases examined. GW packets having large scales that allow them to avoid dissipation at lower altitudes lead to secondary (or higher) self-acceleration events as the packet leading edge amplifies at altitudes above the first event. Initial studies of self-acceleration dynamics for 2D and 3D localized GW packets exhibit additional responses at larger scales accompanying secondary GW generation.