May 20, 2005
Bldg. 21, Rm 183, Noon

SIERRA sounding rocket observations of Alfvenic processes
in the topside auroral ionosphere.

Eric Klatt

ABSTRACT:
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 dE/dB
implied a static field-aligned current sheet configuration.
In the poleward region, the average electric field was much larger,
included time-varying components that exceeded 100 mV/m with
periods of 0.5-5 s, and dE/dB was Alfvenic. The 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, BBELF (broadband, extremely low-frequency) fluctuations
associated with observed Alfven waves had spectral ratios (dE/dB)
appropriate for inertial Alfven waves larger and smaller than the
electron inertial length, but the phase angle differences between
dE and dB indicate mostly propagating Alfven waves for spatial scales
much larger than the inertial length and a transition to stationary
structure for scales near the inertial length. The data are
consistent with the picture of kilometer-scale oblique Alfvenic
arcs that are unstable to current shear-driven instabilities
discussed in previous theoretical work.