next up previous
Next: November 5, 1995 Up: Data Presentation Previous: October 3, 1995

October 4, 1995

Figure 4 displays data recorded 2300 UT on October 4 to 0430 UT on October 5, 1995 (1608-2138 MLT) in the same format as Figure 3. On October 5 the average daily $Kp$ was 3.6, the electrojet produced magnetic perturbations ranging from $\sim$60-700 nT, and the latitude variations of the auroral currents were more dynamic than on October 3-4.

Auroral roar is first detected exclusively at Arviat (71$^\circ$) beginning near 2310 UT when the poleward boundary of the electrojet is also located at $\sim$71$^\circ$. The most intense emissions continue to be recorded at Arviat until 2347 UT. During 2347-2352 UT the latitude of peak emission intensity moves poleward to Baker Lake (74$^\circ$) and then to Taloyoak (79$^\circ$), with the roar emission disappearing first at Churchill and then at Arviat. The poleward edge of the electrojet follows a similar path, expanding from $\sim$69$^\circ$ at 2340 UT to $\sim$76$^\circ$ at 2355 UT.

During 0015-0050 UT the poleward edge of the electrojet retreats equatorward. Over the same time the latitude of the most intense emissions shifts from
Taloyoak (0015 UT) to Baker Lake (0035 UT) to Arviat (0050 UT). Between 0100 and 0130 UT the poleward edge of the electrojet stays near 70$^\circ$, and what little emissions occur remain concentrated at Arviat (71$^\circ$).

From 0130 to 0145 UT the latitude of the peak intensity moves poleward from Arviat to Baker Lake and then to Taloyoak. The electrojet boundary moves from 68$^\circ$ to 76$^\circ$ during this same period and remains above $\sim$72$^\circ$ until 0300 UT. During this time, auroral roar emissions are detected primarily at Baker Lake and Taloyoak with the peak intensity most often at Taloyoak.

After 0305 UT the electrojet boundary shifts poleward, reaching $>$80$^\circ$ at 0335 UT and 0345-0350 UT. The auroral roar also shift poleward, with the highest intensity recorded at Taloyoak. In fact, auroral roar is detected exclusively at Taloyoak from 0320 to 0410 UT, except for two brief periods near 0345 and 0354 UT when emissions are also detected at Baker Lake. A brief burst of intense emissions is detected at Baker Lake just before $\sim$0354 UT, just preceding the equatorward shift in the poleward electrojet boundary at 0355 UT and at about the same time that the equatorial electrojet boundary jumps poleward from 64$^\circ$ to 68$^\circ$ and back to 65$^\circ$.

Two substorm onsets can been seen during this day, a rather weak one at 0130-0145 UT, the radio frequency effects of which extend only as far north as Arviat (71$^\circ$), and a stronger one at 0305-0330 UT, the effects of which extend to Taloyoak (79$^\circ$). One signature of a substorm onset in the PSFR data is a brief intensification of auroral roar emissions before an abrupt cutoff. The poleward boundary of the electrojet expands poleward as the electrojet intensity increases during a typical substorm onset.


next up previous
Next: November 5, 1995 Up: Data Presentation Previous: October 3, 1995


Simon Shepherd 2002-06-05