Statistical Study of Energy Transport and Conversion in Electron Diffusion Regions at Earth's Dayside Magnetopause.

The electron diffusion region (EDR) is a key region for magnetic reconnection, but the typical energy transport and conversion in EDRs is still not well understood. In this work, we perform a statistical study of 80 previously published near X‐line events identified at the dayside magnetopause in Magnetospheric Multiscale data. We find 44 events that clearly present all commonly accepted EDR signatures and use this database to investigate energy flux partition and energy conversion. We find that energy partition is changed inside EDRs, with a 71%–29% allocation of particle energy flux density between electrons and ions respectively. The electron enthalpy flux density is found to dominate locally at all EDRs and is predominantly oriented in the out‐of‐plane direction, perpendicular to the reconnecting magnetic field. We also examine the transition from electron‐ to ion‐dominated energy flux partition further from the EDR, finding this typically occurs at scales of the order of the ion inertial length, larger than the typical EDR size. We then investigate energy conversion and transport and highlight complex processes, with potential non‐steady‐state energy accumulation and release near the EDR. We discuss the implications of our results for reconnection energy conversion, and for magnetopause dynamics in general. Plain Language Summary: Magnetic reconnection is a key plasma phenomenon that occurs in many astrophysical systems, such as in the atmosphere of stars and in the vicinity of magnetized planets like the Earth. It enables rapid conversion of energy as particles gain energy from the magnetic field and are accelerated and heated. In 2015, the 4‐satellite Magnetospheric Multi‐Scale (MMS) mission launched to specifically probe magnetic reconnection close to the Earth. Here we analyze MMS data, first reviewing all previously reported measurements of the very heart of the reconnection region by MMS, and cross‐analyzing them to provide a catalog of 44 confirmed events. We use this catalog to understand how energy is changing during reconnection, finding that energy is mostly deposited to electrons at the heart of the reconnection region. The transport of thermal energy is most important there, and this energy is flowing out of the reconnection region in a direction transverse to the magnetic field. We find that the transfer of energy between field and particles is complex, with temporal effects at play near the reconnection region. These findings bring new insight into the physics of reconnection energetics and have wide implications for wherever reconnection is observed. Key Points: We provide the first comparative statistical study of all previously reported MMS dayside magnetopause EDRs and confirm 44 clear encountersEnergy flux partition changes at the EDR, it is locally dominated by the electron enthalpy flux oriented in the out‐of‐plane directionWe highlight complex field‐particle energy exchange near the EDR where temporal and non linear effects seem play a role [ABSTRACT FROM AUTHOR]