Auroral Poleward Boundary Intensifications: their two-dimensional
structure and the associated dynamics in the Plasma Sheet

Eftyhia Zesta, Larry Lyons, Eric Donovan, Harald U. Frey, Tsugunobu
Nagai

Auroral poleward boundary intensifications (PBIs) have an auroral
signature in ground meridional scanning photometer (MSP) data that
appears as an increase in intensity at or near the magnetic separatrix.
This increase is often seen to extend equatorward through the
ionospheric mapping of the plasma sheet. PBIs are associated with plasma
sheet flow bursts and are thus important to plasma sheet dynamics. We
previously found that equatorward extending PBIs are either north-south
(NS) aligned structures or east-west (EW) arcs that mostly propagate
equatorward. We further investigate the plasma sheet dynamic structures
associated with these two types of PBIs by combining data from the
CANOPUS MSPs, auroral images from the IMAGE spacecraft, and magnetic
field and plasma data from the Geotail spacecraft. We study a period on
January 3, 2001, when a series of PBIs were seen in the MSP data for 2.5
hrs. From simultaneous IMAGE and Geotail data we find that: (a) PBIs
correlate well with plasma sheet fast flows observed within the local
time sector of the PBIs. There can be several PBIs over the longitudinal
range of fast flows in the tail, (b) multiple PBIs can occur over the
whole width of the plasma sheet or in a more restricted local sector
(i.e. only pre-midnight). When PBIs are seen only in a local sector fast
flows are seen only in that local sector as well. Where no PBIs are seen
no fast flows are seen, (c) most of the observed PBIs were EW arcs that
initiated near the poleward boundary and then propagated equatorward.
They often tilted and became mostly NS structures as they propagated
equatorward and duskward, (d) there is a local time dependence on the
type of PBI structure. Most PBIs seem to be narrow structures and
primarily aligned with a line that goes through the 02 MLT and 17 MLT
sectors. This results in PBIs that are NS structures in the postmidnight
sector and EW arcs in the dusk sector. In the premidnight sector (22-00
MLT) PBIs start as EW arcs that then tilt and become primarily NS
structures. These results suggest that the same plasma sheet dynamics
produce EW and NS PBI structures.

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002