The Influence of Mass Diffusion on Vertically Propagating Atmospheric Acoustic-Gravity Waves in the Upper Mesosphere-Lower Thermosphere

Atmospheric acoustic, gravity, and acoustic-gravity waves (AGW) can be generated by various sources of natural and anthropogenic origins. These waves play an important role in the transfer of vertical momentum and heat transport in atmospheres and thus also in defining an atmosphere’s structure. As well, they contribute to the transport/mixing of neutral species deep into the thermosphere despite the effects of dissipative processes (see the works of Fritts and Alexander, 2003; Walterscheid and Hickey, 2012; Vadas and Nicolls, 2012). The nature of their propagation through stratified layers of the atmosphere, especially the mesosphere and lower thermosphere, allows for multi-species effects to become notable due to the transition in dominant species from molecular nitrogen to atomic oxygen. Previous studies demonstrated the effects of thermo-viscous effects for linear wave propagation (Godin, 2014) and nonlinear wave propagation. However, the conditions that lead to interaction between mass-diffusion dissipation terms, competing with nonlinear effects, and their impact on the vertical propagation of AGWs, remained unaddressed.

On the basis of the transport equations that include the Navier-Stokes, heat transfer, and mass diffusion equations (Ern and Giovangigli, 1994), the influence of attenuation on the propagation of acoustic-gravity waves in the atmosphere is analyzed via a parametric study. New dissipative coefficients, thermal conduction, mass-diffusion, thermo-diffusion, and viscous coefficients are solved for via systems of linear equations derived from the Boltzmann Equations with the use of the Chapman-Enskog Expansion. With the use of a modified form of MAGIC (Zettergren and Snively, 2015; Piñeyro, 2018), we then seek to understand the interplay between nonlinear effects and mass diffusion using characteristic wave sources similar to common surface disturbances that induce AGWs under different atmospheric conditions. This work thus considers infrasonic wave sources and propagation alongside high-frequency AGW / GW propagation. The parametric results presented have implications for multidimensional studies, which are discussed, as well as applications to other planetary atmospheres to allow for further understanding of the mechanisms affecting AGW propagation.