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21 Feb/95, 2:30 - 2:32 UT

Again, solar wind speeds were steady at 360 km/s during the event. During or after the event a change of the IMF tex2html_wrap_inline4540 and tex2html_wrap_inline5386 components from a small positive to a negative value of 3 nT occurred as measured by WIND. IMP8 recorded exactly the same pattern at 2:40 UT which therefore positions this IMF change after the event. The tex2html_wrap_inline4548 index at the time of the event was 1.0.

Figure 5.58 shows a region of double-peaked spectra at low latitudes of around tex2html_wrap_inline5730 N from tex2html_wrap_inline5490 E to tex2html_wrap_inline5734 E which the satellite passes from tex2html_wrap_inline5736 to tex2html_wrap_inline5738 . Isolated double-peak spectra are observed at tex2html_wrap_inline5740 and tex2html_wrap_inline5742 as can be seen in Figure 5.59.

Figure 5.58: Map of spectral findings from the Saskatoon and Kapuskasing radars: 21 Feb/95

Figure 5.59: Peak-map with overlaid flight path of the DMSP F12 satellite: 21 Feb/95

The flux/energy graph in Figure 5.60 shows two regions of high flux, one at electron energies of about tex2html_wrap_inline5340 from tex2html_wrap_inline5736 to tex2html_wrap_inline5748 and one at lower electron energies from tex2html_wrap_inline5750 to tex2html_wrap_inline5752 .

Figure 5.60: Average electron energy and flux determined from SSJ/4 instrument measurements: 21 Feb/95

Contrary to the above segmentation into two precipitation regions, Figure 5.61 shows that throughout the period from tex2html_wrap_inline5736 to tex2html_wrap_inline5752 the ionization rate in the F-layer is quite variable. Sharp gradients occur at tex2html_wrap_inline5758 close to an observed double-peak spectrum. The sharp ionization peak at tex2html_wrap_inline5760 is almost exacly coincident with the double peak event that lies on the satellite track at tex2html_wrap_inline5762 . This peak is only a few seconds in width, corresponding to a spatial structure less than about 15 km across.

Figure 5.61: Estimated ionization rates at E- and F-layer heights determined from electron spectra measurements: 21 Feb/95

Figure 5.62 indicates that E-layer conductivities are not much enhanced by the precipitation.

Figure 5.62: Estimated E-layer conductivities from the Robinson model: 21 Feb/95

Velocities in Figure 5.63 are very steady at around tex2html_wrap_inline5766 westward and have been recorded in the area of double-peak spectra occurrence. The double-peak spectra thus are located in a region of eastward current, which one would normally associate with the eastward auroral electrojet. The low tex2html_wrap_inline4548 and the positive tex2html_wrap_inline4540 IMF conditions preceding the event are not consistent with the low latitude of the current and the scatter if the event were in the postnoon sector. However these results occur near magnetic dusk where the influence of the near-midnight substorm region is felt. The analysis of ionospheric velocity maps 30, 20 and 10 minutes before the event indicate that the velocities doubled and an associated velocity shear is built up in the north-south direction.

Figure 5.63: SuperDARN velocity map: 21 Feb/95

next up previous
Next: 25 Feb/951:42 - Up: Morphology during a Complete Previous: 20 Feb/9516:32 -

Andreas Schiffler
Wed Oct 9 10:05:17 CST 1996