Anomalous Cosmic-Ray Helium, Nitrogen and Oxygen in 1996 - Measurements of the ERNE Instrument on-board SOHO
Vainio, R.; Valtonen, E.; Riihonen, E.; Teittinen, M.; Torsti, J.; Mäkelä, P.; Anttila, A.
Abstract
The energy spectra of the anomalous components of helium, nitrogen and oxygen have been measured by the ERNE experiment on board the SOHO spacecraft. During February 28-April 30, 1996, the maximum intensity of anomalous helium was found to be 3.8 × 10-5 cm-2 sr-1 s-1 (MeV nucl-1)-1 in the energy range 10-15 MeV nucl-1. During the period January 26-April 30, 1996, the maximum oxygen intensity was 1.2 × 10-5 cm-2 sr-1 s-1 (MeV nucl-1)-1 at 4-7 MeV nucl-1, and the maximum nitrogen intensity 1.7 × 10-6 cm-2 sr-1 s-1 (MeV nucl-1)-1 at 4-9 MeV nucl-1. These peak intensities are at the same level as two solar cycles ago in 1977, but significantly higher than in 1986. This gives observational evidence for a 22-year solar modulation cycle. A noteworthy point is that the spectra of anomalous nitrogen and oxygen appear to be somewhat broader than in 1977.