Association of north-south Poleward Boundary Intensifications (PBI) orientation 
with plasma sheet flow direction and the IMF

E. Zesta, L. Lyons, E. Donovan, J.B. Sigwarth, H.U. Frey, T. Nagai 


Auroral poleward boundary intensifications (PBIs) are typically seen both in
ground meridional scanning photometers (MSP) and in ground and spacecraft
auroral images. They appear as a localized 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 for the remote monitoring of plasma
sheet dynamics. From the study of simultaneous IMAGE FUV auroral images and
Geotail plasma sheet data we recently found that: (a) PBIs correlate well with
plasma sheet fast flows observed within the local time sector of the PBIs, and
there can be several PBIs over the longitudinal range of fast flows in the tail,
and (b) 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 going from ~02
MLT to ~17 MLT. This results in PBIs that are north-south (NS) structures in the
postmidnight sector and east-west (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. We further found for one event that
the PBI fast flows have a large Vy component resulting from tail convection
during positive IMF By, which offers a possible explanation for the alignment
direction of PBIs. We now use a variety of spacecraft and ground data (Polar
VIS, IMAGE FUV, and ground all-sky images of the aurora, in-situ data from
Geotail, and solar wind data) to investigate the generality of the above
conclusions. We identify NS PBIs and investigate whether (a) there is a clear
distinction in the orientation of the NS PBIs along the 02-17 MLT, the 22-07 MLT
lines, or strictly along the NS meridian, (b) the orientation of the NS PBIs is
correlated with the direction of the plasma sheet convection and thus with the
IMF By direction, and (c) the local time dependence of the PBI orientation in
our previous study is generally observed during all NS PBI periods.

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003