Electron-to-ion Bulk Speed Ratio as a Parameter Reflecting the Occurrence of Strong Electron-dominated Current Sheets in the Solar Wind

Abstract

Abstract Current sheets (CSs) are preferred sites of magnetic reconnection and energy dissipation in astrophysical plasmas. Electric currents in them may be carried by both electrons and ions. In our prior theoretical studies of the CS formation in turbulent plasmas, 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 in which electrons become the main carriers of the electric current and contributors to energy dissipation may form inside or nearby ion-dominated CSs. These structures represent a distinguished type of CSs and should not be mixed up with so-called electron-scale CSs. Current simulations show that such CSs are characterized by the electron-to-ion bulk speed ratio (u e /u i ) increases that can be seen at ion scales according to theoretical predictions and high-resolution observations from the Magnetospheric Multiscale mission. Therefore, applying the u e /u i parameter to the solar wind data may allow locating the strongest electron-dominated CSs with an ordinary spacecraft resolution of 1−3 s. This study shows that, indeed, electron-dominated CSs observed during a period of quiet solar wind conditions at 1 au impact the surrounding plasma, which may be reflected in sharp changes of u e /u i . 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, displaying the same clustering. We conclude that u e /u i may be used as one of the key parameters for statistical studies of CSs in the solar wind and analyzing the role of electrons in them.