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The fine magnetic field structure of two successive plasmoids previously reported is investigated by magnetic rotation analysis using four Cluster satellite data. Between these two plasmoids, opposite trends of curvature radius (Rc) variations of the magnetic field lines from the boundary to the inner part are found. The different variations of Rc...

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... separation of the test tetrahedron is set to 600 km to guarantee that in the benchmark L/D (600 km/1 R E ) has the same value as in above in situ observations (L/D ~ 300km/0.5 R E ~ 0.1). In cylindrical coordinates (Figure 2b), for magnetic fields pro- duced by a straight current, the magnetic unit vector has only one component b ϕ = 1, and the curvature radius is naturally R c = r; in addition, the three components of the magnetic unit vector in the ER model is expressed as Figure 3b) to the sum of the other two components, the angle between the magnetic field, and the current density directions (θ ° ). The two red vertical lines in Figures 3a and Figure 3b indicate the minimum R c and the maximum R c at the central region of the ML and the MFR sepa- rately. ...
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... cylindrical coordinates (Figure 2b), for magnetic fields pro- duced by a straight current, the magnetic unit vector has only one component b ϕ = 1, and the curvature radius is naturally R c = r; in addition, the three components of the magnetic unit vector in the ER model is expressed as Figure 3b) to the sum of the other two components, the angle between the magnetic field, and the current density directions (θ ° ). The two red vertical lines in Figures 3a and Figure 3b indicate the minimum R c and the maximum R c at the central region of the ML and the MFR sepa- rately. In the regions outside the two vertical blue lines in Figure 3a, J N dominates the current inten- sity. ...
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... two red vertical lines in Figures 3a and Figure 3b indicate the minimum R c and the maximum R c at the central region of the ML and the MFR sepa- rately. In the regions outside the two vertical blue lines in Figure 3a, J N dominates the current inten- sity. In Figure 3b, the vertical blue line indicates the time of appearance of faster flow as already shown with the vertical blue line in Figure 1: before the blue line, the R c of the magnetic field lines obeys the trend in Figure 2d and the MFR is force-free; after the blue line, the previous situation is broken by faster flow. ...
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... the regions outside the two vertical blue lines in Figure 3a, J N dominates the current inten- sity. In Figure 3b, the vertical blue line indicates the time of appearance of faster flow as already shown with the vertical blue line in Figure 1: before the blue line, the R c of the magnetic field lines obeys the trend in Figure 2d and the MFR is force-free; after the blue line, the previous situation is broken by faster flow. ...
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... From top to bottom, Figures 3a and 3b show the observations of the two magnetic B z bipolar signatures by the four Cluster satellites, the R c of the field lines in plasmoids, the current density components, the ratio of the main current density component (main current density component is J N in Figure 3a except during the interval indicated by the blue vertical lines and J B in Figure 3b) to the sum of the other two components, and the angle between magnetic field and current density directions. In BRN orthogonal coordinates linked to the magnetic field line, B lies along the magnetic field direction, R lies along the direction of magnetic curvature, and N completes the right-hand orthogonal set, as displayed in Figure 2b. ...
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... From top to bottom, Figures 3a and 3b show the observations of the two magnetic B z bipolar signatures by the four Cluster satellites, the R c of the field lines in plasmoids, the current density components, the ratio of the main current density component (main current density component is J N in Figure 3a except during the interval indicated by the blue vertical lines and J B in Figure 3b) to the sum of the other two components, and the angle between magnetic field and current density directions. In BRN orthogonal coordinates linked to the magnetic field line, B lies along the magnetic field direction, R lies along the direction of magnetic curvature, and N completes the right-hand orthogonal set, as displayed in Figure 2b. ...
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... From top to bottom, Figures 3a and 3b show the observations of the two magnetic B z bipolar signatures by the four Cluster satellites, the R c of the field lines in plasmoids, the current density components, the ratio of the main current density component (main current density component is J N in Figure 3a except during the interval indicated by the blue vertical lines and J B in Figure 3b) to the sum of the other two components, and the angle between magnetic field and current density directions. In BRN orthogonal coordinates linked to the magnetic field line, B lies along the magnetic field direction, R lies along the direction of magnetic curvature, and N completes the right-hand orthogonal set, as displayed in Figure 2b. ...
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... BRN orthogonal coordinates linked to the magnetic field line, B lies along the magnetic field direction, R lies along the direction of magnetic curvature, and N completes the right-hand orthogonal set, as displayed in Figure 2b. As we can see in Figure 3a, it is interesting to note that R c decreases from the boundary (the beginning and ending of the figure) to the inner part of the first plasmoid. R c has a value of about 2 R E at the boundary and a minimum value of 0.4 R E at the B z inflection point (red vertical line). ...
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... c has a value of about 2 R E at the boundary and a minimum value of 0.4 R E at the B z inflection point (red vertical line). In contrast, as shown in Figure 3b, the R c of the magnetic field shows an opposite variation trend; that is, it increases from the outer toward the center (red vertical line) in the re- gion of the MFR before 00:51:46 UT (blue vertical line). R c reaches a maximum of ~0.9 R E at the center. ...
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... Another difference in these two plasmoids is the current density distribution, shown in Figures 3a and 3b. In most re- gions (the regions outside of the two blue vertical lines in Figure 3a) of the first plasmoid except the region near the B z inflection point (the regions between the two blue vertical lines in Figure 3a), the total current intensity is less than 10 nA. ...
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... Another difference in these two plasmoids is the current density distribution, shown in Figures 3a and 3b. In most re- gions (the regions outside of the two blue vertical lines in Figure 3a) of the first plasmoid except the region near the B z inflection point (the regions between the two blue vertical lines in Figure 3a), the total current intensity is less than 10 nA. This value is comparable with the current density in the plasma sheet but is far smaller than that generally encountered in MFR [Slavin et al., 2003b]. ...
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... Another difference in these two plasmoids is the current density distribution, shown in Figures 3a and 3b. In most re- gions (the regions outside of the two blue vertical lines in Figure 3a) of the first plasmoid except the region near the B z inflection point (the regions between the two blue vertical lines in Figure 3a), the total current intensity is less than 10 nA. This value is comparable with the current density in the plasma sheet but is far smaller than that generally encountered in MFR [Slavin et al., 2003b]. ...
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... the region between the two blue lines, J B dominates the current density. The current density in the second plasmoid (Figure 3b) is more intense and mainly lies along the magnetic field direction (|J B |/(|J R | + |J N |) > 1) before 00:51:46 UT (blue vertical line); however, after the blue line, the current density becomes suddenly weaker and is no longer field- aligned. The MRA calculation of current density in the second plasmoid obtains the similar results as the curlometer calcula- tion showed in Henderson et al. [2006]. ...
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... the ideal ML case, the R c is zero at the central axis and has maximum value at the edge, and the ratio of the R c to the maximum R c will gradually decrease from 1 at the edge to 0 at the central axis. In this case, the R c has a maximum value of about 2 R E at the edge (the beginning and ending of Figure 3a) and a minimum value of 0.4 R E at the center (red vertical line). The ratio of the minimum R c to the maximum R c is 0.2 which is small. ...
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... means that the trajectory of Cluster crosses near the center of this ML. On the contrary, the R c variation before the vertical blue line in the second plasmoid (Figure 3b) is similar to the MFR scenario shown in Figure 2d: R c decreases gradually from the inner part to the edge. This trend indi- cates that the magnetic field in this plasmoid becomes more curled with increasing distance from the center. ...
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... The different magnetic configurations in ML and MFR are induced by the different distributions of current density in them. As shown in Figure 3a, most regions (the regions out- side the two vertical blue lines) of the first ML-type plasmoid is current-scarce with two components of J R and J B less than J N except the region near the center, while in Figure 3b, the second MFR-type plasmoid is current-abundant with in- tense field-aligned current. To simplify the discussion, we place an ideal circular two-dimensional ML in a cylindrical coordinate system (Figure 2b), with the ML axis in the Z direction. ...
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... The different magnetic configurations in ML and MFR are induced by the different distributions of current density in them. As shown in Figure 3a, most regions (the regions out- side the two vertical blue lines) of the first ML-type plasmoid is current-scarce with two components of J R and J B less than J N except the region near the center, while in Figure 3b, the second MFR-type plasmoid is current-abundant with in- tense field-aligned current. To simplify the discussion, we place an ideal circular two-dimensional ML in a cylindrical coordinate system (Figure 2b), with the ML axis in the Z direction. ...
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... to the weak total current J T , most of these ML outer regions could be seen as current-free. Obviously, this ML configuration needs a strong current along the central axis to support it just as is observed for J N near the ML center in Figure 3a. ...
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... In the second MFR-type plasmoid, the angles between intense current density and magnetic field direc- tions are in the range of 0 ο À 45° at the leading part of the MFR and 135 ο À 180° at its trailing part before the blue line (Figure 3b). The direction of the current is nearly aligned to the magnetic field lines, so this MFR can be described as nearly force-free. ...

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