Orbit of the Cluster spacecraft on 25 January 2002. The top left panel shows the orbit of Cluster 3 in GSE coordinates, projected onto the x–y plane; the top right shows a projection on the x–z plane; the bottom left panel shows the Cluster 3 orbit in cylindrical coordinates; and the bottom right panel shows a closeup of the spacecraft orbits near the magnetopause in cylindrical coordinates. The position of the magnetopause crossing of Cluster 3 is marked by green circles in all panels, and the positions of the other spacecraft at that same instant are shown the bottom right panels as black, red, and blue circles for Cluster 1, 2, and 4, respectively. A Shue model magnetopause, which has been scaled to agree with the observed Cluster 3 magnetopause crossing, is shown in black in all panels. Specifically, what is shown in the upper panels is the intersection of the magnetopause with the plane of the figure. That is why the green circle, which shows the projection of the magnetopause crossing onto that plane, does not lie on the curve showing the magnetopause.
Solar wind parameters measured by the Wind spacecraft. Panel (a) shows the proton density; (b) the solar wind speed; and (c) the magnetic field magnitude (black), and the GSE (blue), (green), and (red) components.
Data from the Cluster spacecraft on 25 January 2002. The left column shows data from Cluster 1, the middle column Cluster 3, and the right column shows data from Cluster 4. Panels (a-c) show the magnetic field components (blue), (green), (red), and in nanoteslas. The coordinates are in the GSE system. The curves are labelled at the right hand side of each panel. Panels (d-f) show the dynamic pressure for the three spacecraft, respectively. Panels (g-i) show the velocity components in GSE coordinates: (blue), (green), and (red) in kilometers per second. The curves are labelled at the right hand side of each panel. Panels (j-l) show the proton density. Panels (m-o) show the proton temperature. Panels (p-r) show the ratio of the velocity component normal to the magnetopause to the total velocity . Panels (s-u) show the cross-magnetopause proton flux perpendicular to the magnetopause . The red dots in panels (j-u) highlight data points with large flux across the magnetopause (). In all panels, the dashed and solid vertical lines mark the inner and outer boundaries of the transition region, respectively. The two arrows in panel (s) mark the times for which distribution functions are shown in Fig. 10.
Field-aligned electron spectrum (a), (c), and (e) for Cluster 1, 3, and 4, respectively. Omnidirectional ion spectrum for Cluster 1, 3, and 4 are shown in panels (b), (d), and (f), respectively. The ion spectra for Cluster 1 and 3 were measured by the CIS-HIA sensor, and that for Cluster 4 by CIS-CODIF. The electron spectra were measured by the PEACE instrument. The quantity shown on the color scale is the logarithm of the flux in units of cm− 2 s− 1 sr− 1 keV− 1. The dashed and solid vertical lines mark the inner and outer boundaries of the transition region, respectively.
Density measured by Cluster 1 (black) and by Cluster 3 (green) between 10:39 and 10:43. During this period Cluster 3 crossed the magnetopause, while Cluster 1 was located on the magnetospheric side of it. The magnetopause crossing time for spacecraft 3 was identified in magnetic field data as 10:41:23 UT.
Closeup of the Cluster 1 (a) and 3 (b) ion spectra from 10:23 to 10:25. Cluster 3 was located closer to the magnetopause and Cluster 1 farther inside the magnetosphere, as is seen by the orbit plot in Fig. 1.
Color-coded ion temperature along the orbits of Cluster 1 and 3. The spacecraft positions at 10:23:58 have been marked in the figure. The same cylindrical coordinate system as in Fig. 1 is used. Also like in Fig. 1, a scaled Shue model magnetopause is shown in the top right corner in the position where it was encountered by Cluster 3.
Panel (a) shows the angle between the plasma velocity measured by Cluster 3 and the direction from Cluster 3 to Cluster 1. Panel (b) shows the predicted time of flight from spacecraft 3 to 1 based on the velocity measurements by spacecraft 3 (green). Panel (c) shows the density measured by spacecraft 1 (black) and by spacecraft 3 (green). In all panels, the Cluster 3 data, shown by green lines, have been delayed s, corresponding to the dashed line in panel (b).
The upper panels show the perpendicular velocity component (black solid curve) for Cluster 1 (a) and Cluster 2 (b). For comparison, is shown by the red dots. The lower panels (c) and (d) show the perpendicular (black curves) and parallel (blue curves) velocity components. The dashed and solid vertical lines mark the inner and outer boundaries of the transition region, respectively.
Velocity distribution functions for Cluster 1 at 10:21:11 (left) and 10:53:19 (right). The horizontal axis shows the velocity component normal to the magnetopause, and the vertical axis shows the tangential component parallel to the magnetosheath flow direction. The observation times are marked by arrows in panel (s) of Fig. 3.
Rotational discontinuity test. The red curves show in the direction indicated in each panel. The blue curves show in the same direction in panels (a) and (b), and in panels (c) and (d). Cluster 1 results are shown in panels (a) and (c) and Cluster 3 in panels (b) and (d).
A sketch of the plasmoid motion. In the magnetosheath, plasmoids move mostly parallel to the magnetopause, but with an overlaid component inward along the normal direction. Further in, the direction of motion is increasingly inward.
Solar wind parameters from the Wind spacecraft.
Mean and peak cross-magnetopause fluxes during the last 30 min before each spacecraft crossed the magnetopause. The two columns with numerical values show the flux calculated by Eqs. (1)–(4) as described in Sec. IV and by using the Shue model with input data from measurements by the Wind spacecraft to compute the magnetopause normal.
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