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Ann. Geophys., 21, 719-728, 2003
www.ann-geophys.net/21/719/2003/
© European Geosciences Union 2003
Rocket-borne investigation of auroral patches in the evening sector during substorm recovery
M. A. Danielides1 and A. Kozlovsky1,2
1Department of Physical Sciences, P.O. Box 3000, FIN-90014 University of Oulu, Finland
2Sodankylä Geophysical Observatory, FIN-99600 Sodankylä, Finland
Abstract. On 11 February 1997 at
08:36 UT after a substorm onset the Auroral Turbulence 2 sounding rocket was
launched from Poker Flat Research Range, Alaska into a moderately active
auroral region. This experiment has allowed us to investigate evening (21:00
MLT) auroral forms at the substorm recovery, which were discrete multiple
auroral arcs stretched to, the east and southeast from the breakup region, and
bright auroral patches propagating westward along the arcs like a luminosity
wave, which is a typical feature of the disturbed arc. The rocket crossed an
auroral arc of about 40 km width, stretched along southeast direction. Auroral
patches and associated electric fields formed a 200 km long periodical
structure, which propagated along the arc westward at a velocity of 3 km/s,
whereas the ionospheric plasma velocity inside the arc was 300 m/s westward.
The spatial periodicity in the rocket data was found from optical ground-based
observations, from electric field in situ measurements, as well as from
ground-based magnetic observations. The bright patches were co-located with
equatorward plasma flow across the arc of the order of 200 m/s in magnitude,
whereas the plasma flow tended to be poleward at the intervals between the
patches, where the electric field reached the magnitude of up to 20 mV/m, and
these maxima were co-located with the peaks in electron precipitations
indicated by the electron counter on board the rocket. Pulsations of a 70-s
period were observed on the ground in the eastern component of the magnetic
field and this is consistent with the moving auroral patches and the
north-south plasma flows associated with them. The enhanced patch-associated
electric field and fast westward propagation suggest essential differences
between evening auroral patches and those occurring in the morning ionosphere.
We propose the wave that propagates along the plasma sheet boundary to be a
promising mechanism for the evening auroral patches.
Key words. Ionosphere (auroral
ionosphere; electric fields and currents)
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