Measurements of Energy Dissipation in the Electron Diffusion Region

Abstract

Abstract An outstanding question in magnetic reconnection is how the energy being dissipated in the diffusion region. This paper evaluates the quasi‐viscous dissipation in the electron diffusion region (EDR) at Earth's magnetopause by the observations from the Magnetospheric MultiScale mission. We compared two fluid parameters, J · E ˊ and Pi‐D, and found that J · E ˊ and Pi‐D have opposite signs in about half of the examined EDRs. The gyrotropic effect is more important than the nongyrotropic effect for the viscous dissipation in the diffusion region. One intriguing discovery is that electrons are cooled rather than heated in a large portion of the EDRs, with the compressional effect dominates over the viscous effect in electron thermodynamics. Enthalpy flux flowing into or out from the EDR greatly affect the electron entropy variation within the EDR. This study is an important step toward fully resolving the dissipation mystery in reconnection.