SIERRA observations of Alfvénic processes in the topside auroral ionosphere

Details SIERRA observations of Alfvénic processes in the topside auroral ionosphere SIERRA observations of Alfvénic processes in the topside auroral ionosphere

Aug 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jgra..11010s12k&link_type=abstract

Journal of Geophysical Research, Volume 110, Issue A10, CiteID A10S12

Physics

7

Ionosphere: Auroral Ionosphere (2704), Ionosphere: Electric Fields (2712), Ionosphere: Plasma Waves And Instabilities (2772), Ionosphere: Ionosphere/Magnetosphere Interactions (2736), Ionosphere: Current Systems (2721)

Scientific paper

The NASA SIERRA rocket mission was a multiple-payload, auroral plasma physics experiment that flew into a 100 nT auroral substorm at altitudes up to 735 km over the Poker Flat Research Range in Alaska on 14 January 2002. The flight environment was composed of an equatorward region of inverted-V electron precipitation followed by a poleward region of mostly field-aligned suprathermal electron bursts. In the inverted-V region, the measured δE/δB implied a stationary field-aligned current configuration. In the poleward region, the average electric field was much larger, 50 mV/m compared with 20 mV/m, included time-varying components that exceeded 100 mV/m with periods of 0.5-5 s, and δE/δB was Alfvénic. Our multiple-payload observations show that the perpendicular scale size of most of these waves is on the order of a kilometer or less. At smaller scales, broadband, extremely low-frequency (BBELF) fluctuations associated with observed Alfvén waves had spectral ratios (δE/δB) appropriate for inertial Alfvén waves larger and smaller than the electron inertial length (λe = c/ωpe), but the phase angle differences between δE and δB indicate mostly propagating Alfvén waves for spatial scales much larger than λe and a transition to spatial perturbations, embedded in the plasma, for scales near λe. The data are consistent with the model of kilometer-scale oblique Alfvénic arcs that are unstable to the current shear-driven instabilities discussed in previous theoretical investigations, lending support to the conclusion that the observed BBELF fluctuations are likely driven by the wave-associated field-aligned current shear.

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