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 (≤1 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 (E0 < 0.4 keV) and low flux (0.2 erg cm-2s-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.