Skip to main content

The Abundance of Helium in the Source Plasma of Solar Energetic Particles


Studies of patterns of abundance enhancements of elements, relative to solar coronal abundances, in large solar energetic-particle (SEP) events, and of their power-law dependence on the mass-to-charge ratio, \(A/Q\), of the ions, have been used to determine the effective source-plasma temperature, \(T\), that defines the \(Q\)-values of the ions. We find that a single assumed value for the coronal reference He/O ratio in all SEP events is often inconsistent with the transport-induced power-law trend of the other elements. In fact, the coronal He/O varies rather widely from one SEP event to another. In the large Fe-rich SEP events with \(T \approx 3~\mbox{MK}\), where shock waves, driven out by coronal mass ejections (CMEs), have reaccelerated residual ions from impulsive suprathermal events that occur earlier in solar active regions, \(\text{He}/\text{O} \approx 90\), a ratio similar to that in the slow solar wind, which may also originate from active regions. Ions in the large SEP events with \(T < 2~\mbox{MK}\) may be accelerated outside active regions, and have values of \(40 \leq \text{He}/\text{O} \leq 60\). Mechanisms that determine coronal abundances, including variations of He/O, are likely to occur near the base of the corona (at \(\approx 1.1~\mathrm{R}_{\mathrm{S}}\)) and thus to affect both SEPs (at 2 – \(3~\mathrm{R}_{\mathrm{S}}\)) and the solar wind. Other than He, reference coronal abundances for heavier elements show little temperature dependence or systematic difference between SEP events; He, the element with the highest first-ionization potential, is unique. The CME-driven shock waves probe the same regions of space, at \(\approx 2~\mathrm{R}_{\mathrm{S}}\) near active regions, which are also likely sources of the slow solar wind, providing complementary information on conditions in those regions.

This is a preview of subscription content, access via your institution.

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13


Download references


The author thanks Steve Kahler for many helpful discussions of subjects included in this manuscript.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Donald V. Reames.

Ethics declarations

Disclosure of Potential Conflicts of Interest

The author declares that he has no conflicts of interest.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Reames, D.V. The Abundance of Helium in the Source Plasma of Solar Energetic Particles. Sol Phys 292, 156 (2017).

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI:


  • Solar energetic particles
  • Solar flares
  • Coronal mass ejections
  • Solar system abundances
  • Solar wind