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Ann. Geophys., 25, 1629-1652, 2007
www.ann-geophys.net/25/1629/2007/
© European Geosciences Union 2007
Poleward moving auroral forms (PMAFs) revisited: responses of aurorae, plasma convection and Birkeland currents in the pre- and postnoon sectors under positive and negative IMF By conditions
P. E. Sandholt1 and C. J. Farrugia2
1Department of Physics, University of Oslo, Oslo, Norway
2Space Science Center, University of New Hampshire, Durham, USA
Abstract. Using five case studies, we
investigate the dynamical evolution of dayside
auroral precipitation in relation to plasma convection,
classifying it by the
IMF By component and position with respect to noon.
Auroral observations were made
by meridian scanning photometers
(MSPs) and an all-sky camera (ASC) in Ny Ålesund,
Svalbard at 76° MLAT, while the spatial structure of the ionospheric
plasma convection is inferred from SuperDARN radars
and ion drift observations from spacecraft in polar orbit.
The IMF configuration of major interest here is one pointing southward
and with a dominant east-west
component. Our emphasis is on the auroral phenomenon of PMAFs
(poleward moving auroral forms), which
are ionospheric signatures
of pulsed reconnection at the magnetopause.
We distinguish between
PMAFs/prenoon and PMAFs/postnoon. These two activities are found to be
separated
by an auroral form around noon with attenuated emission at 630.0 nm.
We document for the first time that this "midday gap aurora"
appears in the form of a midday auroral brightening
sequence (MABS).
We study the PMAF activity consisting of an
initial brightening phase and the later stages of
PMAF evolution
in relation to plasma convection cells, flow vorticity,
and precipitation boundaries in the prenoon and postnoon sectors
for both By polarities.
Flow channels (PIFs) associated with PMAFs
are strengthened by polarization effects at auroral boundaries.
Addressing the implications of our proposed, extended perspective on dayside
auroral morphology under southeast/west IMF
for M-I coupling associated with pulsed
magnetopause reconnection (FTEs),
we draw inferences on the MLT-dependent geoeffectiveness
(Birkeland current/auroral intensity) of magnetopause
FTEs (subsolar region versus
flanks).
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