Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm21c..02p&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM21C-02
Physics
0310 Airglow And Aurora, 2704 Auroral Phenomena (2407), 2708 Current Systems (2409), 2716 Energetic Particles, Precipitating
Scientific paper
Most satellite data are essentially point observations made along the satellite orbital track. Although reasonable assumptions can be made in many cases, fundamentally, one cannot differentiate between spatial and temporal structures. To overcome this shortcoming we recorded video images of the aurora conjugate to the FAST satellite from an instrumented jet aircraft. A total of 29 flights were made during Moon-down periods in January and February of 1997 and 1998. In each flight the aircraft was flown along the FAST satellite path such that the aurora of interest would be in the magnetic zenith at the time of the pass. A variety of aurorae were encountered between 20 and 23 MLT. We present the main findings from our analysis of these conjunctions. The auroral luminosity measured by the cameras corresponds well with the precipitating energy flux measured by FAST. In the discrete aurora the luminosity is accounted for by energetic electrons, but in the diffuse (evening) aurora equatorward of the discrete arcs proton precipitation can contribute significantly. In relatively quiet multiple arcs, the observed orientation of the arcs agree well with the orientation of the field-aligned current sheets derived from the FAST magnetometer data implying that the currents represent the arc morphology. In dynamic aurora the geometry of the current sheets are more complicated and the relationship does not hold. Complicated electron distribution functions and field measurements are also observed as arcs change morphology and propagate westward. There is a current threshold (at 100 km altitude) of approximately 2.2 μ A/m2 in field-aligned current density for the formation of large spirals as for example often seen in the westward traveling surge. Black aurora is found to be associated with spatially restricted regions within a region of generally isotropic pitch angle distributions in which the strong pitch angle diffusion is suppressed at energies greater than 2 keV. If downgoing electric fields existed in these regions, they were too small for any particle or field measurements on FAST to confirm their existence. In a few cases of flickering aurora the data indicate that the modulating process extends below the altitude of the satellite. The FAST data, with its very high temporal resolution, combined with the auroral video provide a unique data set for the study of small scale temporal and spatial structures in the aurora that has yet to be fully explored.
Peticolas Laura M.
Stenbaek-Nielsen Hans C.
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