Electron Heat Flux in the Near-Sun Environment

We survey the electron heat flux observed by the Parker Solar Probe (PSP) in the near-Sun environment at heliocentric distances of 0.125-0.25 AU. We utilize measurements from the Solar Wind Electrons Alphas and Protons and FIELDS experiments to compute the solar wind electron heat flux and its components and to place these in context. PSP observations reveal that electron heat flux signatures near the Sun have a close correspondence with plasma beta, consistent with regulation by collisionless mechanisms. The magnitude of the heat flux is anticorrelated with solar wind speed, as a result of the lower saturation heat flux in the higher-speed wind. The net heat flux decreases in high-beta regions in the vicinity of the heliospheric current sheet, but in most such cases the omnidirectional suprathermal electron flux remains at a comparable level or even increases, seemingly inconsistent with disconnection from the Sun. The measured heat flux values appear inconsistent with regulation primarily by collisional mechanisms near the Sun. Instead, the observed heat flux dependence on plasma beta and the distribution of suprathermal electron parameters are both consistent with theoretical instability thresholds associated with oblique whistler/magnetosonic modes.