Auroral Emissions at the North Magnetic Pole-A February 17, 1993 Case Study.

Abstract

During the first 12 1/2 hours of February 17, 1993, 21 apparently-isolated events of discrete polar arcs were recorded in broad-band visual light by an all-sky camera and in the blue, green, and red lines by a meridian scanning photometer at Eureka, an observatory near the north magnetic pole (89° magnetic latitude). The polar arcs were located almost exclusively in the dusk sector. Most of the arcs (>60%) were faint (s1 kR in the blue, green, or red lines). The remainder were bright arcs (1-17 kR in the green) associated with energy fluxes of 1-7 erg cm-2s_1 and characteristic energies of -0.6 keV. The average lifetime of an individual polar arc was 8 minutes. One of the 21 identified events of polar arcs was associated with diffuse emissions duskward of the arc. The faint (0.5 kR in the green) diffuse emissions extended from the dusk horizon of the camera up to the arc. They were associated with very soft (Eo < 0.4 keV) and low flux (0.2 erg cm-29-1) particle precipitation. These emissions were probably the optical manifestation of particle entry phenomena reported in the past, namely the location of transpolar arcs at the poleward edge of continuous soft particle precipitation. The lifetime of the diffuse emission (40 min) was much longer than the lifetime of the polar arc (6 min) and it did not follow the duskward motion of the arc. We show a time sequence of a new phenomenon regarding sun-aligned arcs-short lived, antisunward propagating intensifications in the form of bright spots spread over a very small spatial scale along the arc.

Polar ionospheric responses to solar wind IMF changes

“…When the IMF B z is northward, structured electron precipitation often occurs in the polar region, resulting in polar auroral arcs, at very high geomagnetic latitudes (b80 ) that extend some distance in a sun-earth direction (Davis, 1960;Carlson, 1990;Oznovich and McEwen, 1994;Huang et al, 1994). Some of these arcs are very bright and extend across the polar region from the dayside to the nightside of the auroral oval to form a pattern of Greek letter``theta'' (Frank et al, 1982).…”

Drifting F-Layer Patches over the Magnetic Pole.

“…If patch drift motion represents the instantaneous convection direction across the polar cap, as is likely, then the sudden change in direction is due to a change in the IMF By (as discussed by Cannon et al (1991)). There are no IMF data for that time period, but our observations overall for that date (Oznovich and McEwen, 1994) suggest that the IMF Bz and By were highly variable during that period. There were sun-aligned arcs both before and after the 2-hour period from 0900 to 1100 UT when drifting patches were observed.…”

“…3.3 February 17, 1993-0945-1115 UT This was an active night with aurora] sun-aligned arcs (Oznovich and McEwen, 1994) appearing through most of the early hours until 0830 UT and again beyond 1200 UT. In the interval between, from 0945 until 1115 UT, a whole series of F-layer patches appeared.…”

An extended TRANSCAR model including ionospheric convection: simulation of EISCAT observations using inputs from AMIE

“…On 16 February around 21:00 UT, intense ion outflows have been observed by the Akebono satellite and the EISCAT VHF radar in the nighttime auroral zone (Yoshida et al, 2000). On 17 February, at the Canadian Polar Observatory at Eureka (89 • magnetic latitude), auroral Sun-aligned arcs were observed by Oznovich and McEwen (1994), most of them in the early hours until 8:30 UT and again beyond 12:00 UT. In the interval in between, from 9:45 until 11:15 UT, McEwen et al (1995) observed, by optical means and a digital ionosonde, drifting F layer ionization patches.…”