The role of ring current O⁺ in the formation of stable auroral red arcs

Abstract

Coulomb collisions between ring current protons and thermal electrons were first proposed by Cole (1965) as the energy source for stable auroral red (SAR) arcs. Recent observations have shown that the ring current and magnetospheric plasma contain significant amounts of heavy ions (Johnson et al., 1977; Young et al., 1977; Geiss et al., 1978; and others). In fact, the ring current is often dominated by heavy ions at those energies (E ≤ 17 keV) important for Coulomb collisions on SAR arc field lines (Kozyra et al., 1986a). Observations (during four SAR arcs in 1981) of thermal and energetic ion populations by the Dynamics Explorer 1 satellite in the magnetospheric energy source region and nearly simultaneous Langmuir probe measurements of enhanced electron temperatures by Dynamics Explorer 2 within the SAR arc at F region heights have allowed us to examine the role of heavy ions in the formation of SAR arcs. We find that (1) sufficient energy is transferred to the electron gas at high altitudes via Coulomb collisions between the observed ring current ions and thermal electrons to support the enhanced (SAR arc) F region electron temperatures measured on these field lines, (2) the latitudinal variation in the electron heating rates calculated using observed ion populations is consistent with the observed variation in electron temperature across the SAR arc, and (3) in all cases, ring current O+ is the major source of energy for the SAR arcs. This implies a relationship between the heavy ion content of the magnetospheric plasma and the occurrence frequency and intensity of SAR arcs.

An average image of proton plasma pressure and of current systems in the equatorial plane derived from AMPTE/CCE‐CHEM measurements

“…Furthermore, the total energy, contained in the ring current particles, which is of the order of 1023 erg, is sufficiently large to cause appreciable atmosphere ionization or heating if released in a short time. Many effects, like subauroral electron temperature enhancements [Brace et al, 1967], stable auroral red arcs (SAR) [Kozyra et al, 1987[Kozyra et al, , 1997 and energetic neutral and ion precipitating fluxes [Dessler et al, 1961], are observed at midlatitudes as consequences of this energy release. Moreover, the ring current can also act as an energy source contributing to plasma instabilities and wave growth.…”

Subauroral red arcs as a conjugate phenomenon: comparison of OV1-10 satellite data with numerical calculations

“…The rate of energy transfer from the energetic ringcurrent ions to plasmaspheric electrons due to Coulomb collisions has been discussed extensively by Kozyra et al (1987). There is no information available on the ringcurrent population for this storm, and we are therefore forced to assume a heating rate function.…”

“…(A10) of the Appendix. At the present time, waveparticle interactions (Thorne and Horne, 1992;Erlandson et al, 1993;Horne and Thorne, 1993) and Coulomb collisions between ring-current ions (Cole, 1965;Kozyra et al, 1987;Slater et al, 1987;Kozyra and Nagy, 1991;Fok et al, 1995aFok et al, ,b, 1993 and plasmaspheric electrons and ions are the most plausible mechanisms used to explain electron temperature enhancements and the associated SAR arcs. The present work addresses the contribution from this latter process.…”

“…It can be found from Eq. (4) in Kozyra et al (1987) that the value of r is proportional to x e Á À1a2 e , where x e is the electron number density and e is the electron temperature of the plasmasphere. Therefore we selected the additional heating rate as…”

“…Several excitation mechanisms have been proposed to account for the heating of the electron gas in the SAR arc region (Cole, 1965;Cornwall et al, 1971;Rees and Roble, 1975;Kozyra et al, 1987;Kozyra and Nagy, 1991;Thorne and Horne, 1992;Horne and Thorne, 1993). Unfortunately, the theory of these mechanisms is very complicated and we cannot use simple equations for the additional heating rate of the electron gas.…”