Atmospheric gamma rays from solar energetic particles and cosmic rays penetrating the magnetosphere

We detail observations of gamma rays produced by interactions of cosmic ray s and solar-energetic particles on the Earth's atmosphere. The Solar Maximu m Mission (SMM) spectrometer accumulated the quiescent atmospheric spectrum over its full 9-year lifetime and our analysis revealed 20 resolved line f eatures. We compare this spectrum with one collected on October 20, 1989, w hen SMM observed gamma rays produced by shock-accelerated protons that impa cted the atmosphere in the polar region following an intense solar flare an d coronal mass ejection. Observed nuclear-line intensities increased by ove r a factor of 50 during this event. Because this event was on the horizon a nd subtended a limited solid angle as viewed from SMM, the local increase w as several times higher. We compare the gamma ray line energies, widths, an d intensities from the solar event and quiescent atmospheric spectra and di scuss their identifications. From this comparison we confirm direct observa tions that the solar proton spectrum is considerably softer than the spectr um of cosmic rays. Extension of an existing code for calculating solar gamm a ray lines will provide information on the spectra of the protons reaching the Earth's atmosphere and thus on their transport through the magnetosphe re. Broad spectral features found in the spectra are likely to be caused by a multitude of unresolved lines excited by neutron capture in the instrume nt, spacecraft, and Earth's atmosphere.