3.3 The field-aligned currents
In this subsection, we take a closer look at the parallel currents near the Earth. The survey plots of Figures 3 - 7 showed currents connecting from the magnetosphere to the ionosphere, but because of the high density of grid points much of the detail that was present in the data could not be shown. Figure 9 shows frames for t = 21.6, 28.8, 36.0 and 50.4. The data is unfiltered. The resolution of the scenes are 300´ 300 pixels, and the area shown is 6´ 6 RE. Each pixel represents about 120´ 120 km. The red is for currents parallel to B and, blue for antiparallel currents. The currents actually extend all the way to the Earth. The white region surrounding the Earth, indicated by the gray, is an artifact of the program that converts the data from curvilinear to Cartesian representation for display. In all of these panels the color scaling is relative. That is, the maximum and minimum currents in each scene were used to assign the colors, with the most saturated red and blue being assigned to the most intense parallel and antiparallel currents. The intensity of the currents shows a consistent growth until t = 36.0.
The panel for t = 21.6 shows primarily a pair of upward and downward currents, with the downward current equatorward of the upward current. In the t = 28.8 panel the most noticeable feature is the appearance of multiple current filaments of both polarities poleward of the original current pair shown. These currents have a much more filamentary structure and are more intense than the equatorward pair. In the t = 36.0 panel shows the continued poleward progression of the filamentary currents, and also there appears to be a new diffuse current pair that appears equatorward of the currents seen previously. The highest latitude currents are approaching the resolution limit of the grid. Finally, the bottom right panel for t =50.4 at the end of the run shows that the current filaments have retreated pretty well poleward of the region where the we started seeing the field-aligned currents at the start of the run.