Self-Acceleration and Instability of Gravity Wave Packets: 2. Two-Dimensional Packet Propagation, Instability Dynamics, and Transient Flow Responses

Abstract

Results of two-dimensional and narrow three-dimensional (2-D and 2.5-D) simulations of a gravity wave (GW) packet localized in altitude and along its propagation direction employing a new, versatile compressible model are described. The simulations explore self-acceleration and instability dynamics in an idealized atmosphere at rest under mean solar conditions in a domain extending to an altitude of 260 km and 1,800 km horizontally without artificial dissipation. High resolution in the central 2.5-D domain enables the description of 3-D instability dynamics accounting for breaking, dissipation, and momentum deposition within the GW packet. 2-D results describe responses to localized self-acceleration effects, including generation of secondary GWs (SGWs) at larger scales able to propagate to much higher altitudes. 2.5-D results exhibit instability forms consistent with previous 3-D simulations of instability dynamics and cause SGW generation and propagation at smaller spatial scales to weaken significantly compared to the 2-D results. SGW responses at larger scales are driven primarily by GW/mean flow interactions arising at early stages of the self-acceleration dynamics prior to strong GW instabilities and dissipation. As a result, they exhibit similar responses in both the 2-D and 2.5-D simulations and readily propagate to high altitudes at large distances from the initial GW packet. A companion paper examines these dynamics for an initial GW packet localized in three dimensions and evolving in a representative 3-D tidal wind field.