HR: 1330h
AN: SM42A-0595    [PDF]
TI: Conditions Governing High-Latitude Dayside Aurora During IMF $B_y>0$
AU: * Korth, H
EM: haje.korth@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
AU: Anderson, B J
EM: brian.anderson@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
AU: Immel, T J
EM: immel@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, Grizzly Peak Blvd. at Centennial Dr., Berkeley, CA 94720 United States
AU: Frey, H U
EM: hfrey@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, Grizzly Peak Blvd. at Centennial Dr., Berkeley, CA 94720 United States
AU: Mende, S B
EM: mende@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, Grizzly Peak Blvd. at Centennial Dr., Berkeley, CA 94720 United States
AB: In a recent study of IMAGE FUV data, Frey et al. (2003) examined cases of high-latitude dayside aurora caused by precipitating electrons predominantly during northward IMF with a strongly positive IMF By component. Analysis of FAST data showed that the auroral spots coincide with regions of localized upward field-aligned currents (FACs). In order to determine the conditions that control these auroral emissions, we examined field-aligned currents observed by the Iridium constellation for 25~events of prolonged steady IMF orientation with clock angles between $+60^\circ$ and $+90^\circ$. We find that localized FACs are observed under all solar wind conditions but that the occurrence of high latitude aurora are restricted to solar wind proton densities below $4\,\mathrm{cm^{-3}}$ and peak current densities higher than $1.0\,\mathrm{\mu A/m^2}$. These conditions were met for the 11~events with auroral emissions while emissions are not observedduring the remaining 14~events for which these conditions are not met. Our findings can be qualitatively explained with the Knight relation [Knight, 1973], which states that the field-aligned potential drop is directly proportional to the field-aligned current density and inversely proportional to the energy density of the precipitating population. Auroral emissions are generated, if the field-aligned potential drop, which accelerates electrons into the ionosphere, is sufficiently large whereas either low current density or high particle density leads to lower potential and correspondingly weaker aurora. The results also indicate that the particle density on field lines mapping to the upward current region is largely governed by the solar wind density.
DE: 2400 IONOSPHERE
DE: 2407 Auroral ionosphere (2704)
DE: 2409 Current systems (2708)
DE: 2431 Ionosphere/magnetosphere interactions (2736)
DE: 2455 Particle precipitation
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting