Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....99..435i&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A1, p. 435-447
Physics
2
Atmospheric Models, Energy Spectra, Ion Emission, Nitrogen Ions, Oxygen Ions, Particle Precipitation, Auroras, Geomagnetic Latitude, Lyman Spectra, Magnetic Storms, Mass Spectroscopy, Scattering Cross Sections
Scientific paper
Some anomalous auroral emissions, typically observed below 60 deg geomagnetic latitude during large geomagnetic storms, have distinctive spectral characteristics, that have been attributed to energetic ion/neutral particle precipitation. Mass spectrometers on satellites have observed energetic (keV) ion and neutral precipitation (up to 30 erg/sq cm/s) below 60 deg geomagnetic latitude. In this study we used a model to calculate emissions with the characteristics of the incident O(+) energy spectra observed from satellites and compared the emission intensities and intensity ratios of the model calculation to those from the anomalous auroral emission spectra. Using an oxygen transport model with estimated emission cross sections, we calculated the emission altitude distributions, vertically integrated column emission intensities and the spectral profile of atomic oxygen line emissions. The calculated emissions were for the N2(+) and O2(+) first negative (1N), N2 second positive (2P), and N2 Lyman-Birge-Hopfield (LBH) bands; the N I lines at 1493 A, 1744 A, and 8680 A; the N II line at 5005 A, and the O I lines at 1304 A, 1356 A, and 6300 A. Most atomic oxygen line emissions are from primary oxygen atoms traveling downward at a speed of 10(exp 7) and 10(exp 8) cm/s. Because of the high speed at which the atoms travel, most 1D is quenched before emission. Atomic oxygen line spectra at 1304 A and 1356 A display a 1 A Doppler shift and some broadening if viewed from above or below. The emission altitudes and intensities are most sensitive to the choice of elastic scattering cross sections and emission cross sections, respectively. The emission intensity ratios of both the N2(+)1N to N(2P) band and the N2LBH bands to the atomic lines, and the Doppler shift of atomic O lines strongly depend on the energy spectrum of incident O(+). Seasonal and latitudinal model atmospheric differences have least impact. With an energy spectrum of incident O(+), the general model results agree with the observed anomalous auroral emission spectra that were interpreted as being caused by O(+) precipitation.
Ishimoto Michi
Meng Ching I.
Romick Gerald J.
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