Current Status of SAR Arc Observations and Theory
Location
Yosemite National Park
Start Date
2-8-1974 1:45 PM
End Date
2-8-1974 2:00 PM
Description
No serious challenges have appeared in the literature in the past several years to refute the theory of thermal excitation as the explanation of Stable Auroral Red arcs. This theory states that energy from the magnetosphere is brought into the ionosphere via conduction in the electron gas; and that the electron population in the high energy tail (E > 2eV) of the Maxwellian distribution is sufficiently large to excite the D level of atomic oxygen, the upper ^state of the A6300 red line transition. Energy Input rates seldom exceed 0.1 ergs cm-2 sec-1, and are usually smaller. The observational limitation is the ability to extract the thermal excitation component from the total nightglow level, a variable quantity. The occurrence of SAR arcs in the region of the plasmapause, a region of large gradients of Ionization across field lines, suggests that electron heating is produced by plasma instabilities driven by proton fluxes in the energy range 10 to 70 keV. Details of the process must still be considered speculative at this time, although relevant theories have appeared in the literature.
Current Status of SAR Arc Observations and Theory
Yosemite National Park
No serious challenges have appeared in the literature in the past several years to refute the theory of thermal excitation as the explanation of Stable Auroral Red arcs. This theory states that energy from the magnetosphere is brought into the ionosphere via conduction in the electron gas; and that the electron population in the high energy tail (E > 2eV) of the Maxwellian distribution is sufficiently large to excite the D level of atomic oxygen, the upper ^state of the A6300 red line transition. Energy Input rates seldom exceed 0.1 ergs cm-2 sec-1, and are usually smaller. The observational limitation is the ability to extract the thermal excitation component from the total nightglow level, a variable quantity. The occurrence of SAR arcs in the region of the plasmapause, a region of large gradients of Ionization across field lines, suggests that electron heating is produced by plasma instabilities driven by proton fluxes in the energy range 10 to 70 keV. Details of the process must still be considered speculative at this time, although relevant theories have appeared in the literature.