On the radial force balance in the quiet time magnetotail current sheet

Using Time History of Events and Macroscale Interactions spacecraft observations of the quite magnetotail current sheet within the r ∈[9,35] R E region ( r is the radial distance from Earth and R E is Earth's radius), we investigate the thermal plasma pressure distribution along the magnetotail. Taking advantage of flapping motions of an ensemble of current sheets at various distances, we estimate the current density magnitude j y (in GSM coordinates). Comparing the tension force j y B z ( B z is the magnetic field component) with the radial gradient of the plasma pressure demonstrates that this gradient is only a small fraction, ∼10–15%, of the Ampere force exerted on the cross‐tail current, in the r > 15 R E region. We also estimate the contribution of the electron temperature anisotropy to the pressure balance: in the r > 15 R E region the corresponding force can balance only 10–15% of the observed tension force j y B z . Thus, we conclude that about 70% of the tension force is not balanced by the combination of isotropic radial pressure gradient or the electron anisotropy. We discuss mechanisms that could be responsible for balancing the magnetotail current sheet.