| The Stable Auroral Red (SAR) arc's neay monochromatic emission at 6300(ANGSTROM) is the ionospheric signature of an energy transfer process spanning tens of thousands of kilometers--the energy source being in the equatorial plasmasphere and the ultimate energy sink being in the F region. The coplanar DE-1 and -2 satellites have made it possible to obtain nearly simultaneous particle and field measurements in the source and sink regions along a common flux tube. 31 coordinated data sets were compiled during which DE-1 was at high altitudes and DE-2 was at F-region heights during traversals of SAR arc field lines on dates identified by ground based photometry. Among other new observational signatures, SAR arcs are colocated with: (1) thermal density enhancements at high altitudes, distinct from and, at times, outside of the normal plasmasphere, and (2) invariant latitude-limited bands of intense plasmaspheric hiss. The following conclusions were drawn from the results of various theoretical and statistical investigations. (1) Changes in the position and magnitude of the subauroral electron temperature peak in response to changing geomagnetic conditions can account for the occurrence statistics of SAR arcs. (2) The soft electron fluxes, precipitating over SAR arcs, have sufficient energy to establish the elevated (SAR arc) electron temperatures. (3) Observed tens of key ring current O('+) can supply sufficient energy to thermal electrons via coulomb collisions to power a SAR arc. (4) The presence of heavy ions drastically modifies the generation and propagation characteristics of ion cyclotron waves so that instead of being broad-band (as originally assumed), wave growth occurs in frequency-limited bands, which are, at times, very narrow. The propagation characteristics in each of these frequency bands have consequences for the damping of these waves to the thermal plasma. (5) Ion cyclotron wave onset is not correlated with the plasmapause density gradient but wave growth occurs with reasonable growth rates throughout the entire range of L shells considered (L = 3.0-6.6), even in the presence of low cold plasma densities. (6) Landau damping of plasmaspheric hiss by thermal electrons is proposed as a possible new mechanism for SAR arc energization. |
