Physics
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002georl..29l..51m&link_type=abstract
Geophysical Research Letters, Volume 29, Issue 12, pp. 51-1, CiteID 1609, DOI 10.1029/2001GL014143
Physics
9
Magnetospheric Physics: Storms And Substorms, Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Energetic Particles, Precipitating, Trapped, Magnetospheric Physics: Auroral Phenomena (2407)
Scientific paper
Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six-hour period, during which a reasonably intense substorm occurred. HENA and the FUV proton auroral imager (SI-12) monitor emissions which are representative of trapped and precipitating magnetospheric proton fluxes, respectively. For several hours prior to substorm onset, measurements of the fluxes of lower energy (10-16 and 16-27 keV) magnetospheric Energetic Neutral Atoms (ENA-s) by HENA and precipitating auroral protons by FUV SI-12 show strong similarities, with the implication that, in general, proton precipitation is controlled by a steady pitch angle diffusion process. Less similarity is seen between ENA-s and the auroral electron precipitation, which is monitored with the FUV Wideband Imaging Camera. Prior to substorm onset, ENA intensity at large radial distance (L > 8) is reduced while the overall integrated ENA flux increases signifying earthward motion and accumulation of the plasma. About 20 minutes before onset, the auroral fluxes decrease while the ENA intensity continues to grow. The observations are consistent with a pre-onset increase in plasma pressure in the inner magnetosphere without an increase in precipitation showing more efficient trapping perhaps by the distorted nightside magnetosphere. At substorm onset the increase in precipitation intensity is very sudden while the more gradual intensification of the energetic ENA-s continues. At onset the electron aurora shows an increase in intensity of one order of magnitude, while the increase in precipitating proton flux is only 50%. The intensification of the precipitation is relatively short lived (~10 minutes) while the ENA substorm enhancements last about an hour.
Frey Harald U.
Gérard Jean-Claude
Immel Thomas J.
Mende Stephen B.
Mitchell Donald G.
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