Turbulence, gravity waves, and instability dynamics observed in polar mesospheric clouds

The proposed research would address small-scale gravity wave, instability, and turbulence dynamics that play central roles in the transport and deposition of energy and momentum throughout the atmosphere. These dynamics are key to defining the large- and smaller-scale structure and variability of the MLT, and their neutral and ionospheric influences extending to higher altitudes. Despite their importance, and numerous previous studies, these dynamics are poorly understood at present. Multiple rocket and ground-based studies have provided important advances defining larger-scale environments and gravity waves, the types and scales of instabilities, and measures of the intensity and variability of turbulence at smaller spatial scales. However, no previous experiment has simultaneously defined 1) the spatial context of the driving gravity wave and instability dynamics over extended horizontal scales, 2) the transition from larger-scale instabilities to turbulence, and 3) the evolving instability and turbulence character extending to the turbulence “inner” scale continuously in time throughout the event. Serendipitous imaging of small-scale instability and turbulence structures in polar mesospheric clouds (PMCs) by star cameras supporting the EBEX stratospheric balloon experiment has demonstrated the potential for such observations. These images reveal instability and turbulence dynamics extending from a few km to ~10-20 m scales (pixel resolution of 3 m) and offer a new window on these dynamics that were not previously possible with any measurement technique. The keys to this sensitivity lie in the very thin PMC layer brightness where advection causes strong PMC thinning and imaging from above atmospheric turbulence at lower altitudes. Our proposed experiment would expand PMC imaging capabilities spatially and temporally. New imaging using very-high-resolution (50 Mpixel) detectors and co-aligned wide and narrow fields of view (FOV) would extend horizontal spatial coverage from ~100 km to ~10-m scales with imaging resolution as high as 2 m. A fixed anti-sun viewing platform would allow tracking of entire events throughout their evolution extending many buoyancy periods (e.g., an hour or longer) with 2-s resolution. High-resolution modeling of gravity wave, instability, and turbulence dynamics that has already yielded tantalizing comparisons of simulated and observed dynamics would be employed to guide quantification of the observed events. The flight program would utilize a small or mid-size constant-pressure balloon flown from McMurdo Station, Antarctica for a flight of 1-2 weeks allowing one orbit around the Antarctic vortex in Austral summer. A launch window from 15/12/2017 to 15/01/2018 would guarantee high sensitivity by our imagers to the multi-scale dynamics revealed in PMC imagery. The experiment would leverage EBEX imaging heritage, the proven CSBF solar power and course pointing systems, and electronics and software to minimize risk in cost and the development timescale. The entire payload would weigh ~1000 lbs, facilitating a relatively simple and cost-effective launch. Minimum telemetry would be needed to evaluate imager performance during the mission, with data stored onboard until retrieval of the payload following the measurement program. The payload would be delivered to the NASA balloon facility in Palestine, TX for testing and shipping to McMurdo ~4 months prior to the anticipated launch window. The proposed research would have specific relevance to goals 2 and 4 in the recent Heliophysics Decadal Survey, Solar and Space Physics: A Science for a Technological Society: - Determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs, - Discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe.