The response of auroral absorption to substorm onset: Superposed epoch and propagation analyses

Details The response of auroral absorption to substorm onset: Superposed epoch and propagation analyses The response of auroral absorption to substorm onset: Superposed epoch and propagation analyses

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11605312k&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue A5, CiteID A05312

Physics

Magnetospheric Physics: Energetic Particles: Precipitating, Magnetospheric Physics: Substorms, Ionosphere: Auroral Ionosphere (2704), Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Ionosphere: Ionospheric Dynamics

Scientific paper

The response of high-energy particle precipitation to substorm onset is investigated using observations of cosmic noise absorption by a 7 × 7 beam imaging riometer in Kilpisjärvi, Finland, and substorm onset information obtained from the IMAGE satellite. A new method is developed for automatic detection of absorption responses to substorm onsets. Superposed epoch analysis shows that absorption exhibits some fading prior to and a clear response preceding substorm onset. These features are interpreted as being due to the stretching of magnetic field lines and a rapid dipolarization during the late growth phase of a substorm. A distinct dependence on substorm onset location is discovered with response delay increasing with distance from substorm onset and all responses to closest substorms (within 250 km) preceding substorm onset by 1-5 min. The absorption propagation is further examined using the average velocity from the onset to the riometer location as well as instantaneous velocities for a short period of time when substorm-enhanced absorption reaches the field of view. Comparison of the two velocity estimates shows that the absorption propagation is slower and oriented in more poleward directions away from substorm onset, with some evidence of near instantaneous expansion in zonal directions over large distances of ˜2000 km from onset followed by a slower expansion primarily in poleward and westward directions. The observations suggest that during substorms precipitating electrons in the high-energy part of the spectrum behave differently from their low-energy counterparts and that they exhibit some evidence of predictable behavior.

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