Electron energetics in the expanding solar wind via Helios observations. Issue 10 (3rd October 2015)

• Record Type: Journal Article
• Authors: Štverák, Štěpán; Trávníček, Pavel M.; Hellinger, Petr
• Is Part Of: Journal of geophysical research. Volume 120:Issue 10(2015:Oct.)
• Page Start: 8177
• Page End: 8193
• Publication Date: 2015-10-03
• Subjects: solar wind -- electrons energetics; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2015JA021368
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We present an observational analysis of electron cooling/heating rates in the fast and slow solar wind between 0.3 and 1 AU. We fit electron velocity distribution functions acquired in situ by Helios 1 and 2 spacecraft by a three‐component (core‐halo‐strahl) analytical model. The resulting radial profiles of macroscopic characteristics (density, temperatures, and heat fluxes) are employed to examine properties of theoretical energy balance equations and to estimate external cooling/heating terms. Our analysis indicates that in contrast to solar wind protons the electrons do not require important heating mechanisms to explain the observed temperature gradients. The electron heating rates are actually found to be negative for both the slow and fast solar wind, namely, due to the significant degradation of the electron heat flux with increasing radial distance from the Sun. Cooling mechanisms acting on electrons are found to be significantly stronger in the slow wind than in the fast wind streams. Key Points: No external heating mechanisms are required for solar wind electrons Required heating is provided by degradation of the electron heat flux Electron energy is largely transported from parallel to perpendicular direction