Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm21b..05s&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM21B-05
Other
2704 Auroral Phenomena (2407), 2712 Electric Fields (2411)
Scientific paper
We examine the physical processes that cause the field-aligned acceleration of plasma particles in the auroral region above the Earth. A data and modeling study has been carried out to examine the acceleration mechanisms that operate in the auroral zone primary current region and to identity the magnetospheric drivers of these acceleration mechanisms. The data portion of the study involves the use of satellite data from the Fast Auroral SnapshoT (FAST) and Polar satellites when the two satellites were in approximate magnetic conjunction in the auroral region. For these events FAST in the midst of the auroral zone and Polar is above the auroral zone in the near-Earth plasma sheet. For these events Polar is used to determine the conditions in the magnetotail that are occurring when field-aligned acceleration is measured by FAST in the auroral zone. For the modeling portion of the study a long-system particle in cell simulation is then used to model the magnetically connected region between the two satellites to determine the physical mechanisms that cause field-aligned plasma acceleration. The data and simulation results indicate that there are three main acceleration mechanisms operating in the primary current region of the auroral zone: (1) kinetic Alfvén waves with a parallel electric field component that propagate into the auroral region as Poynting flux from the magnetotail, (2) relatively strong quasi-static parallel potential drops (parallel electric fields) formed by the inflow of high energy plasma from the magnetotail, and (3) relatively weak double-layer potential drops in regions of field-aligned current. Although these mechanisms all occur in regions of upward directed field-aligned current, they have been found to sometimes occur together and other times separately, usually depending on latitude or magnetic activity. For example, the strong quasi-static potential drops seem to occur more commonly at the poleward edge of the auroral region at higher latitudes and is associated with ionospheric ion outflows, whereas the other mechanisms can occur at somewhat lower latitudes in the auroral zone and are not neccesarily associated with ion outflows. The results found thus far tend to support the overall contention that ultimately it is processes in the magnetotail that lead to discrete aurora, however, it appears to be not a single process, but several.
Ashour-Abdalla Maha
Kletzing Craig A.
Richard Robert
Schriver David
Strangeway Robert J.
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