May 2, 1997

Figure 8 shows the footprint of FAST during its orbit (2745) on May 2, 1997. This orbit was a perigee pass of the Northern Hemisphere, and the altitude of the spacecraft was $\sim$600-800 km. The footprint of FAST passes from the polar cap into the auroral zone near several of the PSFR ground stations during the period $\sim$0648-0652 UT ($\sim$2345-0100 MLT). The vertical dashed lines in Figure 6 indicate when the footprint of FAST is at the same latitude as the ground stations. The solid vertical line marks the time when the footprint of FAST passes the polar cap boundary, indicated in Figures 10a-10c by a dramatic increase in electron energy flux at 0651:00 UT ($\sim$70$^\circ$). The agreement of this boundary and the poleward edge of the electrojet inferred from magnetometer data (upper dashed line in Figure 6g) is within 1$^\circ$ latitude.

Figure 10d suggests that during the conjunction the intensity of the emissions is greatest at Churchill (69$^\circ$), which lies at the poleward boundary of the auroral precipitation to within the resolution of the ground-based receivers. An inverted-V structure extending to nearly 10 keV, shown in Figure 10a, is centered near 69$^\circ$ latitude implying that energetic electrons are present at the latitude of the emissions. Also present on field lines near the location of the most intense auroral roar are upgoing loss cone (180$^\circ$) and downgoing beam (0$^\circ$) distributions (Figure 10c) which are possible sources of a plasma instability which may generate auroral roar Weatherwax:95, Yoon:96.