The solar latitude and radial dependence of the anomalous cosmic-ray helium component.
Abstract
Observations are presented of the spatial intensity gradients of 11-20-MeV per nucleon anomalous helium made with Pioneer 10 and Pioneer 11 over the radial range 1-11.3 AU for Pioneer 10 and to a heliographic latitude of 16 deg at 3.75 AU for Pioneer 11. Evidence is found for a significant gradient in heliographic latitude, with flux increasing away from the equatorial plane at the rate of about 2% to 3% per degree of latitude. This result shows that the common assumption of spherical symmetry for solar modulation is incorrect. By comparison with gradients measured for 29-67-MeV per nucleon helium and for 11-20-MeV and 29-67-MeV protons, it is found that both the radial and latitudinal gradients of the low-energy anomalous helium are the largest of those measured. The implications of these results for the origin of the anomalous component and for solar modulation are briefly discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1979
- DOI:
- 10.1086/182887
- Bibcode:
- 1979ApJ...227L.147M
- Keywords:
-
- Helium;
- Interplanetary Medium;
- Solar Cosmic Rays;
- Solar Wind;
- Kinetic Energy;
- Latitude;
- Pioneer Space Probes;
- Radial Distribution;
- Solar Protons;
- Space Radiation;
- Cosmic Rays:Helium;
- Cosmic Rays:Solar Modulation