The Earth's atmosphere supports a broad spectrum of waves that are generated by meteorological processes, including convection, instability of flows, and wind over mountains. This project investigated gravity waves (also known as buoyancy waves, with periods of minutes to hours, and wavelengths of tens to thousands of kilometers) and very low frequency acoustic waves (much like sound waves, but with oscillation periods of minutes rather than small fractions of a second). Gravity waves in particular are important for their effects on flows and structure of the atmosphere. They propagate upward and outward from their sources, carrying fluxes of energy and momentum, and eventually drive strong effects as they impact the atmosphere above. Thus, gravity waves enable weather in the troposphere to influence "Space Weather" in the upper-atmosphere and near-Earth space environment (thermosphere and ionosphere). 

 The Intellectual Merit of this project was defined by needs to investigate the "coupling" enabled by gravity waves under realistic conditions, and to simulate how we observe them from the ground or space. We considered case studies that were controlled or idealized, to simulate scenarios of how waves propagate, interact, or are observed. These were designed to improve specific understanding of physical processes. We also considered case studies inspired by observations, including waves generated by flow over mountains or by convective storms. The observations included imaging of Earth's airglow layers, especially the infrared glow of excited Hydroxyl molecules at 85 km, as well as measurements by laser remote sensing of temperatures and densities throughout the stratosphere and mesosphere. These measurements were conducted by collaborators via instruments on the ground or in airplanes.

The models we used for simulating atmospheric wave dynamics were continuously improved. They were extended to three dimensions and tohigher resolutions; new models of wave sources were added, to better describe physical processes; and more-realistic perturbations to atmosphericdensities were enabled by new solution techniques. A new capability of the model was also developed to simulate cylindrical wave fields, much like those observed routinely above thunderstorms as "concentric" (circular) gravity and acoustic waves that can extend throughout the upper mesosphere, thermosphere, and ionosphere.

The model development proved extremely useful, enabling new applications for simulating waves in the ionosphere, and resulting in several papers over the course or the project. This has had impacts in other disciplines, for the simulation of waves generated by severe weather or seismic hazard events. The model now also is being used to perturb the ionosphere, via collaborative work with other members of the science community and at Embry-Riddle, enabling new comparisons of dynamics observed via radio remote sensing techniques. 

Modeling capabilities to simulate optical measurements of the mesosphere were extensively developed and improved as part of this project, too. To compare wave perturbations in the model with those observed, we used our models to simulate wave disturbances to hydroxyl airglow at ~85 km, the sodium layer at 75-105 km, and the green emission of atomic oxygen at ~96 km. A student also developed complementary methods to simulate how layers could be imaged from ground or from space, e.g., to capture synthetic "images" of atmospheric emissions for different fields of view including from moving platforms. These capabilities are now being generalized to apply to new problems, for gravity wave imaging from space for pending observational missions.

As this was a Career Development project, it also supported extensive Broader Impacts in outreach and education. It provided assistantship support for two Ph.D. students, support for diverse undergraduate students, and for the contributions of one postdoctoral research associate. Participants in the project were involved in presenting and publishing results, e.g., at conferences and in refereed journals (>15 papers to date at the time of this report). The project also enabled the PI to supervise the undergraduate and masters theses of another student, who was supported externally for their work.

Broader Impacts in public outreach included presentations shared with the local community via Embry-Riddle's established Astronomy Open House events. An evening lecture was given to the community titled "An Astronomer's Trash is an Aeronomer's Treasure: The Nighttime Glow of Our Dynamic Atmosphere", describing the techniques by which we measure atmospheric dynamics through imaging the glow of atmospheric chemical processes. This, and prior events, also included demonstrations of infrared hydroxyl airglow imagers outside, to show the ambient gravity wave structures present across the night sky.  

Broader Impacts in education included support for the development of a PhD level special topics course (EP711) in Computational Atmospheric Dynamics. This course evolved over three separate deliveries in 2012, 2014, and 2018. It included extensive example codes and demonstrations and, in 2018, involved students in the development of toy atmospheric dynamics model. This code was used by students to reproduce several classic examples from published results, and serves as a useful demonstration for the dynamics of waves in the atmosphere.

Last Modified: 03/15/2019
Modified by: Jonathan B Snively