tokens: to the formula J = n e e ( V i − V e ), where n e is the electron number density and e is the elementary coulomb charge, respectively. Inside the first current sheet, both MMS2 and MMS4 observed mainly out-of-plane electron current J M ′ (Figures 2 (d), (n)). The current densities associated with the reversal of magnetic field component B L ′ peak at 0.7 μ A m −2 and 0.4 μ A m −2 , respectively. Similar trends to electron velocities mean that the current is mainly carried by electrons. Multispacecraft timing analysis (Schwartz 1998 ; Dunlop et al. 2002 ) indicates that the current sheet moves sunward in the current sheet normal direction (where N = L ′ M ′ N ′ (0.3747, 0.0649, 0.9249)) with a speed of 52 km s −1 . The derived normal direction is identical with the N ′ calculated from minimum variance analysis. The duration for the current sheet is ∼0.18 s (∼05:57:08.6 and ∼05:57:08.78 UT). Thus, the thickness of the current sheet is calculated to be 52 km s −1 × 0.18 s = 9.36 km ∼5.5 d e , where d e is the electron inertial length. In the turbulent magnetosheath, similar intense small-scale current sheets are favorable sites for electron-only reconnection (Stawarz et al. 2019 ). Four-spacecraft timing analysis can also be applied to gain quantitative information about the orientation and motion of the flux rope. In the case of a cylindrically symmetric flux rope, it can be shown that the times at which each spacecraft observes the peak field strength define a plane that is perpendicular to the tetrahedron direction of motion and contains the axis of the flux rope. The flux rope is found to be moving at v ∼ 43.5 km s −1 along n = (0.83, 0.26, 0.49) GSM relative to MMS. The velocity of the flux rope is found to be mainly in the x – z plane, indicating that the axis of the structure is nearly in the y direction. This orientation is also consistent with the result calculated by MVA also shown previously. As mentioned above, the flux rope crossing time is 4 s during 05:57:07 UT and 05:57:11 UT. This corresponds to a crossing distance of 174 km based on the normal speed of 43.5 km s −1 of the flux rope, or 2.26 d i . This indicates that the spacecraft are observed an ion-scale flux rope. As previously analyzed, the spacecraft are slightly off-center when crossing the flux rope. This means that any estimate of the flux rope size is a lower bound. MMS2 observed well-defined parallel electric fields (Figure 2 (f)), which indicated the invalidation of the ideal electron frozen-in condition ( E ′ = E + V e × B = 0). The electron dissipation measure ( J · E ′) is calculated in Figure 2 (j) based on current densities and electric field in the electron frame. J · E ′ is positive within the current sheet and is close to zero when MMS crossed outside the exhaust region. The electric field structure is parallel to the background magnetic field at MMS2. The dissipation is positive and basically all dominated by . The energy dissipation is mainly
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