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

This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15±17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He‡ ions (three major ions: O‡, H‡, and He‡, and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the di€usion of NO‡ and O2 ions and O…D† and the revised electron cooling rates arising from their collisions with unexcited N2; O2 molecules and N2 molecules at the ®rst vibrational level. The updated model includes the option to use the models of the Boltzmann or nonBoltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the ®rst ®ve vibrational levels of N2 were calculated. The calculated distribution is highly nonBoltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N2. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modeled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzmann vibrational distribution of N2. The e€ect of using of the O…1D† di€usion results in the decrease of 4±6% in the calculated integral intensity of the northern hemisphere and 7±13% in the calculated integral intensity of the southern hemisphere. It is found that the modeled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coecients of O‡…4S† ions with the vibrationally excited nitrogen molecules and quenching of O‡…2D† by atomic oxygen than the modeled intensities of the northern hemisphere.