Global Distributions of Lateral Gravity Wave Propagation from a 20-year Climatology of Directional Gravity Wave Momentum Fluxes Derived from 3-D Satellite Observations

Atmospheric gravity waves (GWs) play a key role in the transfer of energy and momentum between layers of the Earth's atmosphere, and their accurate representation in global circulation models (GCMs) is needed to simulate realistic dynamical phenomena such as the Quasi-Biennial Oscillation (QBO) and the behaviour of the wintertime stratospheric vortex, including Sudden Stratospheric Warmings (SSW) events. However, not all aspects of GW dynamics are currently included in operational GCMs. One current topic of interest is the role of lateral (oblique) propagation of GWs that have significant directional components orthogonal to the prevailing wind vector. Constraining the lateral momentum carried by such waves is an unanswered question of high importance to the global stratospheric GW momentum budget. Here we use a recently developed 20-year global climatology of directional GW momentum flux in the stratosphere, derived from 3-D satellite observations from AIRS/Aqua, to address this question. We first focus on the lateral propagation of GWs around the wintertime polar vortices. By tracking the location of the edge of the vortex, we are able to study the longitudinal distribution of GW momentum poleward and equatorward of the vortex edge. We find that, despite not being apparent in the zonal mean, there is significant meridional propagation of GW momentum into the northern polar vortex. We then quantify this effect during SSW events and explore the relationship between GW momentum and different modes of planetary wave (PW) activity, especially when PW nodes are located over GW hotspots. Finally, we consider the global distribution of GW momentum both in the direction of, and orthogonal to, the prevailing wind vector to provide the first global observational constraints on the momentum budget of laterally propagating GWs in the stratosphere.