Computer Science
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995ldef.symp..113t&link_type=abstract
In NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1 p 113-127 (SEE N95-23796 07-9
Computer Science
1
Earth Orbital Environments, Energetic Particles, Fluence, Geomagnetism, Heavy Ions, Interplanetary Medium, Ion Charge, Solar Corpuscular Radiation, Spaceborne Experiments, Energy Spectra, Iron, Long Duration Exposure Facility, Low Earth Orbits, Solar Flares
Scientific paper
It has long been known that low-energy solar energetic particles (SEP's) are partially-ionized. For example, in large, so-called 'gradual' solar energetic particle events, at approximately 1 MeV/nucleon the measured mean ionic charge state, Q, of Fe ions is 14.1 +/- 0.2, corresponding to a plasma temperature of approximately 2 MK in the coronal or solar-wind source material. Recent studies, which have greatly clarified the origin of solar energetic particles and their relation to solar flares, suggest that ions in these SEP events are accelerated not at a flare site, but by shocks propagating through relatively low-density regions in the interplanetary medium. As a result, the partially-ionized states observed at low energies are expected to continue to higher energies. However, up to now there have been no high-energy measurements of ionic charge states to confirm this notion. We report here HIIS observations of Fe-group ions at 50-600 MeV/nucleon, at energies and fluences which cannot be explained by fully-ionized galactic cosmic rays, even in the presence of severe geomagnetic cutoff suppression. Above approximately 200 MeV/nucleon, all features of our data -- fluence, energy spectrum, elemental composition, and arrival directions -- can be explained by the large SEP events of October 1989, provided that the mean ionic charge state at these high energies is comparable to the measured value at approximately 1 MeV/nucleon. By comparing the HIIS observations with measurements in interplanetary space in October 1989, we determine the mean ionic charge state of SEP Fe ions at approximately 200-600 MeV/nucleon to be Q = 13.4 plus or minus 1.0, in good agreement with the observed value at approximately 1 MeV/nucleon. The source of the ions below approximately 200 MeV/nucleon is not yet clear. Partially-ionized ions are less effectively deflected by the Earth's magnetic field than fully-ionized cosmic rays and therefore have greatly enhanced access to low-Earth orbit. Moreover, at the high energies observed in HIIS, these ions can penetrate typical amounts of shielding. We discuss the significance of the HIIS results for estimates of the radiation hazard posed by large SEP events to satellites in low-Earth orbit, including the proposed Space Station orbit. Finally, we comment on previous reports of low-energy below-cutoff Fe-group ions, which some authors have interpreted as evidence for partially-ionized galactic cosmic rays. The LDEF flux levels are much smaller than the corresponding fluxes in these previous reports, implying that the source of these ions has an unusual solar-cycle variation and/or strongly increases with decreasing altitude.
Adams James H. Jr.
Beahm Lorraine P.
Boberg Paul. R.
Kleis Thomas
Tylka Allan J.
No associations
LandOfFree
Results from the Heavy Ions In Space (HIIS) experiment on the ionic charge state of solar energetic particles does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Results from the Heavy Ions In Space (HIIS) experiment on the ionic charge state of solar energetic particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Results from the Heavy Ions In Space (HIIS) experiment on the ionic charge state of solar energetic particles will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1635506