Small-Scale Structure in the Auroral Thermosphere Determined from Rocket and Ground-Based Observations during the CODA and ARIA Set of Experiments

Details Small-Scale Structure in the Auroral Thermosphere Determined from Rocket and Ground-Based Observations during the CODA and ARIA Set of Experiments Small-Scale Structure in the Auroral Thermosphere Determined from Rocket and Ground-Based Observations during the CODA and ARIA Set of Experiments

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa21a..01w&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SA21A-01

Physics

0310 Airglow And Aurora, 0358 Thermosphere: Energy Deposition : : : : : : : : : : : : : : :, 0355 Thermosphere: Composition And Chemistry, 0358 Thermosphere: Energy Deposition

Scientific paper

A set of rocket and ground-based experiments were carried out between 1992 and 2000 at Poker Flat Alaska in the CODA and ARIA experiments to study the state of the thermosphere during primarily diffuse auroral heating events. Both instrumented payloads and chemical release payloads were launched to measure the compositional and wind properties of the lower thermosphere, generally in the altitude region between 90 and 200 km, in order to study the response to small-scale forcing and the gradients in the forcing that existed within the auroral oval. Contrary to conclusions based on early models that predicted enhanced winds over a large range of altitudes, the ARIA results showed large winds in a narrower height range near 100 to 120 km with a vertical scale of only 10 to 20 km. The wind speeds were also smaller than the theoretical predictions except in the most disturbed conditions. Measurements over a range of activity levels from the set of rocket experiments have shown a transition from quiet-time tidal winds with peak speeds of approximately 100 m/s to sub-storm winds with wind speeds up to 250 m/s and strong shears in the lower E-region. Richardson numbers associated with the strong wind shears have been well below the usual instability threshold of 0.25, implying strong instability and turbulence generation in the flow and photographs of the chemical release plumes are suggestive of Kelvin-Helmholtz instabilities. Several different techniques were used to measure the composition in the lower thermosphere during these experiments with varying degrees of success. These included in situ rocket measurements of atomic oxygen using resonance lamp techniques, nitrogen and molecular oxygen using a neutral mass spectrometer, and the O/N2 ratio using rocket-borne and ground-based optical remote sensing techniques. The most striking aspects of these observations are the temporal variability and large magnitude of the atomic oxygen depletions that far exceed model expectations. The contributions these experiments have made to our understanding of the small-scale structure in the lower thermosphere and the questions remaining unanswered will be reviewed.

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