Evolution and Instability Dynamics of Gravity Wave Packets of Limited Horizontal Extent.

Vertically propagating gravity waves (GWs) experience a variety of dissipation processes in the real atmosphere, including viscous damping and dynamic instability. Prior work employing an anelastic deep atmosphere numerical model examined GW breaking due to self acceleration (SA) with vertically confined wave packets in simple (isothermal) and complex thermal environments. While these studies demonstrated the nature and importance of SA for GW propagation, they were limited to wave packets of infinite horizontal extent in a periodic domain. This work examines the consequences of that assumption through the modeling of GW packets of limited horizontal and vertical extent. A number of packet geometries, wide and narrow, 2D and 3D, are considered for GWs of various length scales and frequencies and the impact of the packets' scales on the resulting instabilities, and especially on secondary GWs, are examined. A most significant impact of confining the wave packet horizontally deals with secondary wave generation. When secondary waves are generated in a periodic domain their scales are limited to those of the initial wave and the resulting instability scales. For horizontally localized wave packets secondary wave scales are also determined by the packet geometry, rather than just the GW breaking dynamics, resulting in large scale waves capable of reaching thermospheric altitudes. Secondary wave amplitudes, as well as scales, are shown to depend on the underlying packet geometry.