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) (first negative) 3914-¿ and N2(2P)(second positive)- 3371-¿ emission rate observed during a mid-latitude aurora over Logan, Utah (41¿N,111¿W), on September 21-22, 1982. Heavy particle precipitation had previously been invoked to explain the anomalously high populations in the upper vibrational levels of the N2+(1 N) system that are evident in the observed emissions. The N2(2 P) 3371-¿ emission rate in the observed aurora was a factor of 4-7 less than the observed 3914-˚ 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: first, the neutral atmosphere now includes N2 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% N2 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.