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Figure 8.6. Dawn flank pass on June 11, 2001, showing the magnetic field magnitude for a series of magnetopause crossings. (Adapted from Dunlop and Balogh, 2004).

tations, which follow the expected magnetopause shape. A selection of crossings is shown in Table 8.2 and covers 8.5 hours. There is therefore a significant spread in thickness between each encounter. Table 8.2 shows the approximate time of each crossing, the mean MVAB normal, the velocity profile (expressed as before as the mean velocity for each spacecraft pair), the traversal time across the current layer for each of the four spacecraft and the corresponding estimated thickness, Di, at each spacecraft (according to Di = viAti, i = 1,2,3,4, where the vi are estimated from Arij ■ n). Although there is a significant spread in velocities (ranging from —1 to 135 kms-1), and significant acceleration (all velocity profiles are smoothly changing over the array), the small differences in D at each spacecraft are all within the uncertainties, for each of the crossings (within ±200 km). If the mean velocity, or the timing result (assuming constant velocity), is used with the Ati, the spread of Ds are much larger (±900 km).

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