Electron-to-ion bulk speed ratio as a parameter reflecting the occurrence of strong electron-dominated current sheets in the solar wind

Abstract

Current sheets (CSs) are preferred sites of magnetic reconnection and energy dissipation in collisionless astrophysical plasmas. Electric currents in them may be carried by both electrons and ions. In our prior theoretical studies of processes associated with the CS formation in turbulent plasmas, for which we utilized fully kinetic and hybrid code simulations with ions considered as particles and electrons - as a massless fluid, we found that electron-dominated CSs may form inside or nearby ion-dominated CSs. Electrons become the main carrier of the electric current and contributors to energy dissipation in electron-dominated CSs. These magneto-plasma structures represent a distinguished type of CSs and should not be mixed up with so-called electron-scale CSs. Our simulations show that such CSs are characterized by the electron-to-ion bulk speed ratio Ue/Ui increases. Theoretical predictions and high-resolution observations from the MMS mission suggest that strong electron-dominated CSs can be seen at ion scales. Therefore, we suggest that applying the Ue/Ui parameter to the solar wind data may allow locating the strongest electron-dominated CSs with an ordinary spacecraft resolution of one-three seconds at least approximately. The results show that, indeed, an impact of electron-dominated CSs on the plasma observed during a period of quiet solar wind conditions at 1 AU may be associated with sharp changes in Ue/Ui. Electron-dominated CSs are found to be localized in the vicinity of ion-dominated CSs identified via changes in the magnetic field and plasma parameters Ue/Ui, displaying the same clustering. We conclude that Ue/Ui may be used as one of key parameters for probing CSs in the solar wind and the role of electrons in them.