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

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

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm42b0605z&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM42B-0605

Physics

2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions, 2744 Magnetotail, 2764 Plasma Sheet

Scientific paper

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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