Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm31a0738c&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM31A-0738
Physics
2455 Particle Precipitation, 2700 Magnetospheric Physics, 2716 Energetic Particles, Precipitating, 2736 Magnetosphere/Ionosphere Interactions, 2788 Storms And Substorms
Scientific paper
Global distributions of precipitating electron average energy and energy flux inferred from Polar Ultraviolet Imager (UVI) data and simultaneous FAST particles and fields measurements are used to study auroral intensifications during magnetic storms. A strong enhancement of the diffuse aurora is shown to occur near storm sudden commencement, typically associated with the arrival of a solar wind pressure pulse, marking the initiation of magnetic storms. A consequence of this is to enhance the background ionospheric conductivity through increased auroral particle inputs. During the initial phases of magnetic storms diffuse aurora and field-aligned electron beams dominate. Inverted-V structures, if present at this time, are typically weak (peak energies <= 1 keV) in comparison to those seen during non-storm periods. Discrete auroral arcs tend to appear with increasing frequency toward the end of the main phase and storm recovery. These observations suggest that under conditions of enhanced ionospheric conductivity, the low altitude, auroral acceleration region and quasi-electrostatic field-aligned potential drops play less of an important role in producing the observed auroral precipitation. Instead, processes occuring in the magnetospheric source regions such as pitch angle scattering and Alfvénic acceleration appear to be more dominant during storm periods. Our results are consistent with previous statistical studies demonstrating that aurora are less intense under conditions of enhanced ionospheric conductivity. The background ionospheric conductivity is an important initial condition for auroral dynamics.
Brittnacher Mitchell Jay
Carlson Carl W.
Chua Damien H.
Germany Glynn A.
Parks George K.
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