Magnetic Reconnection Energy Fluxes in the Near-Sun Heliospheric Current Sheet as Observed by Parker Solar Probe

Abstract The Heliospheric Current Sheet (HCS) is a fundamental feature of the heliosphere, playing a key role organizing the magnetic structure of the solar wind. In contrast to observations previously made through the majority of the heliosphere, Parker Solar Probe has recently revealed that the HCS is typically reconnecting in the inner heliosphere. This provides a new opportunity to study reconnection dynamics in large-scale current sheets and assess how this is different from smaller systems such as Earth’s magnetosphere. We use Parker data to explore HCS reconnection energy partition in two case studies from Encounter 07 and 08. In both cases, we find that in the exhaust, the proton enthalpy flux density is largest, with significant contributions from the proton kinetic energy flux density and electron enthalpy flux density. In contrast, the exhaust Poynting flux density is small in both events. The size and stability of the HCS allows for a control volume analysis to be performed, thus allowing us to estimate changes in energy flux during reconnection. This analysis shows that energy is primarily transferred from the magnetic field to the protons, manifested as the kinetic energy of the exhaust and proton heating. Although the exhaust electron enthalpy flux density is significant, the incoming and outgoing electron enthalpy fluxes are found to be similar, and there is minimal electron heating. The small contribution of the Poynting flux in the outflow may be an important feature of HCS reconnection, with implications for reconnection in large-scale solar and astrophysical current sheets more generally.