Abstract
<p><span>Electric fields (<strong>E</strong>) play a fundamental role in facilitating the exchange of energy between the electromagnetic fields and the changed particles within a plasma. </span>Decomposing <strong>E</strong> into the contributions from the different terms in generalized Ohm's law, therefore, provides key insight into both the nonlinear and dissipative dynamics across the full range of scales within a plasma. Using the unique, high‐resolution, multi‐spacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent electric field<strong> </strong>spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to <strong>E</strong> over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub‐ion scales. The strength of the non‐ideal electron pressure contribution is stronger than expected from linear kinetic Alfvén waves and a partial anti‐alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents within the turbulence. The relative contributions of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping <strong>E</strong> for the intervals examined in this study. Overall, the sum of the Ohm's law terms and measured <strong>E</strong> agree to within ∼ 20% across the observable scales. The results both confirm a number of general expectations about the behavior of <strong>E</strong> within turbulent plasmas, as well as highlight additional features that may help to disentangle the complex dynamics of turbulent plasmas and should be explored further theoretically.</p>
Highlights
Turbulent dynamics are characterized by nonlinear interactions that transfer energy between fluctuations at different length scales within a fluid, often from large to small scales, generating multiscale gradients and facilitating the dissipation of the fluctuations
The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to E over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub-ion scales
The role of generalized Ohm's law in shaping the turbulent electric field spectrum from MHD to electron length scales is examined for the first time observationally using the unique capabilities of MMS in Earth's magnetosheath
Summary
Turbulent dynamics are characterized by nonlinear interactions that transfer energy between fluctuations at different length scales within a fluid, often from large to small scales, generating multiscale gradients and facilitating the dissipation of the fluctuations. When expressed in single-fluid variables, the terms in Ohm's law highlight the underlying dynamics operating in the plasma across the magnetohydrodynamic (MHD), sub-ion, and electron scales. Et al, 2018; Macek et al, 2019; Shuster et al, 2019; Torbert et al, 2016; Webster et al, 2018) missions have directly observed EHall at small-scale current sheets and revealed the nonideal E, which enables magnetic reconnection, is mainly associated with EPe with a weaker contribution from Einertia. These results are in agreement with previous studies of laboratory reconnection (Brown et al, 2006; Cothran et al, 2005).
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