A Caltech Library Service

Elemental Composition of Solar Energetic Particles


Cook, Walter Richardson, III (1981) Elemental Composition of Solar Energetic Particles. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/04wf-f966.


The Low Energy Telescopes on the Voyager spacecraft are used to measure the elemental composition (2 ≤ Z ≤ 28) and energy spectra (5 to 15 MeV /nucleon) of solar energetic particles (SEPs) in seven large flare events. Four flare events are selected which have SEP abundance ratios approximately independent of energy/nucleon. The abundances for these events are compared from flare to flare and are compared to solar abundances from other sources: spectroscopy of the photosphere and corona, and solar wind measurements.

The selected SEP composition results may be described by an average composition plus a systematic flare-to-flare deviation about the average. For each of the four events, the ratios of the SEP abundances to the four-flare average SEP abundances are approximately monotonic functions of nuclear charge Z in the range 6 ≤ Z ≤ 28. An exception to this Z-dependent trend occurs for He, whose abundance relative to Si is nearly the same in all four events.

The four-flare average SEP composition is significantly different from the solar composition determined by photospheric spectroscopy: The elements C, N and O are depleted in SEPs by a factor of about five relative to the elements Na, Mg, Al, Si, Ca, Cr, Fe and Ni. For some elemental abundance ratios (e.g. Mg/O), the difference between SEP and photospheric results is persistent from flare to flare and is apparently not due to a systematic difference in SEP energy/nucleon spectra between the elements, nor to propagation effects which would result in a time-dependent abundance ratio in individual flare events.

The four-flare average SEP composition is in agreement with solar wind abundance results and with a number of recent coronal abundance measurements. The evidence for a common depletion of oxygen in SEPs, the corona and the solar wind relative to the photosphere suggests that the SEPs originate in the corona and that both the SEPs and solar wind sample a coronal composition which is significantly and persistently different from that of the photosphere.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Vogt, Rochus E.
Thesis Committee:
  • Vogt, Rochus E. (chair)
  • Buffington, Andrew
  • Goldreich, Peter Martin
  • Walker, Robert Lee
Defense Date:3 November 1980
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory80-5
Funding AgencyGrant Number
Record Number:CaltechTHESIS:10072014-083229203
Persistent URL:
Related URLs:
URLURL TypeDescription ItemArticle in CaltechAUTHORS
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8670
Deposited By: Benjamin Perez
Deposited On:07 Oct 2014 16:53
Last Modified:16 Apr 2021 22:29

Thesis Files

PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page