The role of energetic O⁺ precipitation in a mid‐latitude aurora

Abstract

We show that fluxes of precipitating energetic O + that have been observed by satellites in the topside ionosphere can explain the magnitude of the N2+(1 N) (fixst negative) 3914-fit and N2(2 P) (second positive) 3371-fit emission rate observed during a mid-latitude aurora over Logan, Utah (41 ø N, 111øW), on September 21-22, 1982. Heavy particle precipitation has previously been invoked to explain the anomalously high populations in the upper vibjational levels of the N2+(1 N) system that are evident in the observed emissions. The N2(2 P) 3371-A emission rate in the observed aurora was a factor of 4-7 less than the observed 3914-fit emission rate, whereas the rate is a factor of 2 less for a typical electron aurora. A model is used to investigate the impact of precipitating heavy ions on the atmosphere. The model has been improved over previous models in three ways: fixst, the neutral atmosphere now includes N 2 as well as O. Second, measured values rather than theoretical values are used for the elastic scattering differential cross sections, and third, emission rates from energetic O and N2 by heavy particle collisions and their "ionization by-product" low-energy secondary electrons are evaluated. The measured cross sections are smaller than those of the previous models and more strongly forward scattering than the values used in our previous studies, allowing the energetic atoms to penetrate more deeply into the atmosphere. As a result, the peak energy deposition is lowered to approximately 180 km from the 270-to 350-km peak of the earlier calculations. The bulk of the energy of the precipitating flux goes into heating of the neutral atmosphere (-,-82%), while a significant fraction (-,,16%) of the energy is carried by an upward moving neutral escape flux. The escape flux is 13% N 2 and 87% O. The remaining 3% of the incident O + energy goes into ionization and excitation. The nocturnal thermospheric heating rate and ionization rate during one of these events can be equivalent to the daytime EUV heating and ionization rates. We conclude that the characteristics of the observed spectrum can be explained by energetic O + precipitation to within the uncertainties of the inputs to the model.

Density Perturbations in the Upper Atmosphere Caused by the Dissipation of Solar Wind Energy

“…Here they constitute an energy source for the subauroral region (e.g. Galperin et al 1966;Prölss 1973;Torr and Torr 1979;Kozyra et al 1982;Torr et al 1982;Ishimoto et al 1986;Schröder andPrölss 1991, Prölss 1992;Fang et al 2007a, b;and references therein). Second, ring current ions heat the electron gas of the plasmasphere, and part of this energy is transferred to the ionosphere via heat conduction.…”

Charge transfer of keV O+ ions with atomic oxygen

“…First, it is directly applicable to the precipitation of keV energy O* ions into the upper atmosphere which, between 200 and 600 km, consists primarily of atomic oxygen [Shelley et al, 1972;Sharp et al, 1976aSharp et al, , 1976b. During geomagnetic storms the energy carried by these precipitating ions can be quite large, and the detailed behavior of the precipitating O* flux is dependent on the magnitude of the various chargechanging cross sections and on the angular distribution of the scattered neutral products [Bisikalo et al, 1995;Ishimoto et al, 1986Ishimoto et al, , 1992. In an entirely different context, O*-O charge transfer, at thermal energies of the order of 0.1 eV, controls the diffusion of O* ions in the upper atmosphere and hence its structure and dynamics.…”

Ring Current Decay

“…QUTAN et al (1990) considered a more realistic loss-cone distribution for the ring current ions using a 1D hybrid Darwin code and, in addition, consider the effects of both energetic and thermal O+ on the heating of the thermal plasma. They find that thermal He+ is heated more quickly and isotropically in cases where the loss cone is large, and more slowly and anisotropically in the ISHIMOTO et al (1986ISHIMOTO et al ( , 1987 of the neutral heating but were able to place an upper limit of 100K on heating due to neutral precipitation during these storms.…”

“…The relative magnitudes of each of these inputs depends on the species (H, He, O) involved. The energy input into the thermosphere from these precipitating ENA can be quite considerable, a significant fraction of the normal solar EUV input on the dayside (ISHIMOTO et al, 1986). Details on the atmospheric consequences will be presented in later sections of this review.…”