Figure 1

Wind measurements of the ion flow, the magnetic field components, and density during the encounter with an active reconnection region. Further away from the $X$ line $v_y$ and $v_z$ remain small, while the ion outflow speed, $|v_x|$, approaches the Alfvén speed of $400\mathrm{k}\mathrm{m}/\mathrm{s}$.Reuse & Permissions

Figure 2

(a) Illustration of the magnetic geometry and the trajectory of Wind. The green arrows indicate the flow of magnetic flux towards and away from the $X$ line. At locations away from the $X$ line the in-plane magnetic field approaches values of about 10 nT. Besides the in-plane magnetic fields, an out-of-plane guide magnetic field, $B_y=6\mathrm{n}\mathrm{T}$, was also observed. The red arrows illustrate the electrostatic electric field trapping the thermal electrons within the ion diffusion region (the yellow area). (b) An example of a passing electron guiding center trajectory reaching the location of the Wind spacecraft. (c) An example of a trapped electron trajectory. The electron bounces back and forth along a field line, while slowly drifting with the magnetic field towards the $X$ line.Reuse & Permissions

Figure 3

(a)–(c) Electron pitch angle distributions measured by the 3D plasma and energetic particle instrument [25] on the Wind spacecraft at locations indicated in Fig. 2. Each line represents the phase-space density for a given energy; the respective energies are given on the right of the figure. In (a) the blue parts correspond to trapped electrons, and the red parts correspond to passing electrons. At sufficiently high energies the electron orbits become unmagnetized, leading to pitch angle scattering; this effect reduces the level of anisotropy observed above 6 keV [the green parts in (a)]. (d)–(i) Theoretical distributions calculated for locations [inferred from the measured values of $(B_x,B_z)$] corresponding to the data in (a)–(c). The distributions in (d)–(g) correspond to the center of the diffusion region ($t=08:00:22\mathrm{U}\mathrm{T}$) calculated with increasing values of the trapping potential (${\Phi }_0\in \{0,300,900,1150\}\mathrm{V}$). The best match to the data in Fig. 3a is obtained with ${\Phi }_0=1150\mathrm{V}$. The distributions in (h) and (i), also obtained with ${\Phi }_0=1150\mathrm{V}$, correspond to the Wind observations in the outflow region [see (b) and (c)].Reuse & Permissions