Electron heat conduction in the solar wind: Transition from spitzer-härm to the collisionless limit

S. D. Bale, M. Pulupa, C. Salem, C. H.K. Chen, E. Quataert

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


We use a statistically significant set of measurements to show that the field-aligned electron heat flux q ∥ in the solar wind at 1 AU is consistent with the Spitzer-Härm collisional heat flux q sh for temperature gradient scales larger than a few mean free paths LT ≳ 3.5λfp. This represents about 65% of the measured data and corresponds primarily to high β, weakly collisional plasma ("slow solar wind"). In the more collisionless regime λfp/L T ≳ 0.28, the electron heat flux is limited to q /q 0 ∼ 0.3, independent of mean free path, where q 0 is the "free-streaming" value; the measured q does not achieve the full q 0. This constraint q /q 0 ∼ 0.3 might be attributed to wave-particle interactions, effects of an interplanetary electric potential, or inherent flux limitation. We also show a βe dependence to these results that is consistent with a local radial electron temperature profile Te ∼ r that is a function of the thermal electron beta α = α(βe) and that the β dependence of the collisionless regulation constraint is not obviously consistent with a whistler heat flux instability. It may be that the observed saturation of the measured heat flux is a simply a feature of collisional transport. We discuss the results in a broader astrophysical context.

Original languageEnglish (US)
Article numberL22
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Jun 1 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • solar wind
  • stars: winds, outflows


Dive into the research topics of 'Electron heat conduction in the solar wind: Transition from spitzer-härm to the collisionless limit'. Together they form a unique fingerprint.

Cite this