The Unusual Time History of Galactic an Anomalous Cosmic Rays in the Heliosphere over the Deep Solar Minimum of Cycle 23/24
Abstract
The continuing Quiet Sun of the cycle 23/24 solar minimum has resulted in cosmic ray intensity time-histories at 1 AU that are very different from those of the 1965 and 1987 solar minima at the same phase of the 22 year heliomagnetic cycle. Instead of the sharp intensity peak of these earlier cycles, the cosmic ray intensity displays a broad plateau followed by an on-going increase that has now lasted for 1.4 years. Over the cycle 19 and 21 solar minima there was a suppression of the cosmic ray intensity at rigidities below 0.5 GV while at neutron monitor energies (72 GeV) the intensity was 3-5% higher than in qA>0 cycle. For cycle 23/24 in 2009.5 the 200 MeV/n He intensity is 25% higher than its 1987 and the neutron monitor data from the North-West University 4 Station Network is within 1.5% of those of 1987. However, the intensity of 13.5 MeV/n ACR oxygen intensity is a factor of 2 below its 1987 level. These complex spectral differences are clearly caused by the decrease in strength of the interplanetary field below the level of previous minima and the relatively high inclination of the heliospheric current sheet that persisted until ~ 2009.3 before decreasing to lower values. In the heliosheath cosmic ray data from Voyager 1 and 2 are showing significant increases that reflect the changes that are occurring in the solar wind and magnetic fields in the distant heliosphere. The relative behavior of 10 MeV GCR electrons and 150-380 MeV/n He suggest these particles follow a different route entering the heliosphere than the higher energy cosmic rays. At this time the deep solar minimum is continuing so further changes in the cosmic ray time histories can be expected.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.U34A..07M
- Keywords:
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- 2100 INTERPLANETARY PHYSICS;
- 2104 INTERPLANETARY PHYSICS / Cosmic rays