Mapping prenoon auroral structures to the magnetosphere

All-sky auroral images acquired at Ny-Alesund were used in conjunction with observations of a Polar overflight on November 30, 1997, to determine wher e prenoon, 0900-1000 magnetic local time (MLT) auroral structures map to th e outer magnetosphere. Polar observations at midaltitudes are used to const rain the mapping between the aurora and the magnetosphere. The Tsyganenko 9 6 magnetic field model (T96), driven by interplanetary conditions and Dsr, is used for that mapping. When the T96 model is driven by conditions on thi s day, the open/closed field line boundary maps 2-3 degrees lower in latitu de than observed for this day. By making an ad hoc adjustment to match the location of the model open/closed field line boundary to observations, we f ind that the agreement with other aspects of the observations is also impro ved. These include (1) Polar observations of the dayside extension of the b oundary plasma sheet (BPS) (structured low-energy electrons, detected in a region of sunward convection and region 1 field-aligned currents) mapped to the ionosphere in a region of discrete aurora, (2) Polar observations of t he central plasma sheet thigh-energy electron precipitation) maps to diffus e green auroral emissions equatorward of the discrete aurora, and (3) Polar electric field observations are consistent with convective motions of the auroral forms and changing interplanetary magnetic field (IMF) conditions. When the all-sky images are mapped into the magnetosphere, we find that the discrete aurora identified with the BPS mapped to the outer dawnside edge of the magnetosphere. This mapping indicates that earlier Geotail, reports of a sunward flowing mixing region in the equatorial magnetosphere [Fujimot o et al., 1998] is really within the dayside extension of the BPS, compatib le with both the low-altitude BPS observations of Newell and Meng [1992] an d type 4 dayside aurora of Sandholt et al. [1998]. Since the Polar observat ions place the sunward flowing mixing region as a source of region 1 curren ts for this IMF By positive case [Farrugia et al., this issue], these resul ts extend the;source of the region 1 currents from the antisunward flowing low-latitude boundary layer into the sunward flowing BPS, commensurate with Yamauchi et al. [1998] and Sonnerup [1980].