Mesospheric Bore Evolution and Instability Dynamics Observed in PMC Turbo Imaging and Rayleigh Lidar Profiling Over Northeastern Canada on 13 July 2018

Abstract

Two successive mesospheric bores were observed over northeastern Canada on 13 July 2018 in high‐resolution imaging and Rayleigh lidar profiling of polar mesospheric clouds (PMCs) performed aboard the PMC Turbo long‐duration balloon experiment. Four wide field‐of‐view cameras spanning an area of ~75 × 150 km at PMC altitudes captured the two evolutions occurring over ~2 hr and resolved bore and associated instability features as small as ~100 m. The Rayleigh lidar provided PMC backscatter profiling that revealed vertical displacements, evolving brightness distributions, evidence of instability character and depths, and insights into bore formation, ducting, and dissipation. Both bores exhibited variable structure along their phases, suggesting variable gravity wave (GW) source and bore propagation conditions. Both bores also exhibited small‐scale instability dynamics at their leading and trailing edges. Those at the leading edges comprised apparent Kelvin‐Helmholtz instabilities that were advected downward and rearward beneath the bore descending phases extending into an apparently intensified shear layer. Instabilities at the trailing edges exhibited alignments approximately orthogonal to the bore phases that resembled those seen to accompany GW breaking or intrusions arising in high‐resolution modeling of GW instability dynamics. Collectively, PMC Turbo bore imaging and lidar profiling enabled enhanced definition of bore dynamics relative to what has been possible by previous ground‐based observations, and a potential to guide new, three‐dimensional modeling of bore dynamics. The observed bore evolutions suggest potentially important roles for bores in the deposition of energy and momentum transported into the mesosphere and to higher altitudes by high‐frequency GWs achieving large amplitudes.

Kelvin‐Helmholtz Billow Interactions and Instabilities in the Mesosphere Over the Andes Lidar Observatory: 1. Observations

“…PMC imaging also has the ability to see very small features, even finer (below 20 m pixel resolution) than the best current airglow imaging. PMC imaging is hampered, though, by the thickness of the brightest portion of the PMC, often a km thick or less (Fritts et al, 2020), that lessens the chance of PMC imaging revealing the entire vertical extent of the instability.…”

A technical description of the Balloon Lidar Experiment (BOLIDE)

“…As demonstrated in Fig. 7 and in more detail in the overview paper by Fritts et al (2019) and the study by Fritts et al (2020), lidar measurements acquired by the BOLIDE instrument during the PMC Turbo mission yielded high-resolution backscatter profiles of PMC. All requirements (see Table 1) were met, and the performance surpassed that of the largest ground-based lidar systems.…”

“…We note that Kaifler et al (2013) and Ridder et al (2017) present PMC backscatter profiles at higher resolution of 30 s and 40 m, but no information on the detection threshold is given. A subset of the data in Kaifler et al (2013) is shown at a resolution of 0.33 s × 25 m. We want to highlight that BOLIDE data can be processed at even higher resolutions, albeit at the cost of a higher detection threshold as compared to the standard resolution of 30 s × 100 m. Examples with a resolution of 10 s × 20 m are presented in Fritts et al (2020). Figure 8 demonstrates the high-resolution capabilities of the BOLIDE instrument.…”

“…A description of the PMC Turbo gondola and its power and communication systems can be found in Kjellstrand et al (2020).…”

The PMC Turbo Balloon Mission to Measure Gravity Waves and Turbulence in Polar Mesospheric Clouds: Camera, Telemetry, and Software Performance

“…We have published an overview paper ( Fritts et al, 2019 ), describing GWs, associated instabilities, and the larger atmospheric context of our observations. We have also published a study of two successive mesospheric bores imaged by PMC Turbo ( Fritts et al, 2020 ). The PMC Turbo hardware enabled analysis on an area of ~75 × 150 km over ~2 hr while also resolving the bore and instability features with scales down to ~100 m. This allowed for improved resolution of bore dynamics relative to ground-based observations.…”