FGM measurements of a Directional Discontinuity
Directional Discontinuity (DD) measured by the FGM instrument on all four Cluster spacecraft in the solar wind, free of foreshock activity. From top to bottom the plot shows the Bx, By, Bz components and magnitude of the DC magnetic field (Cluster 1: black; Cluster 2: red; Cluster 3: green; Cluster 4: blue).
Time lags between the different spacecraft, used by the triangulation method, are clearly visible in every panel. A significant increase of the Interplanetary Magnetic Field magnitude is visible in the bottom panel.
Knowing that |Bn| is small (not shown) as any other case of this statistical study (see also 'Four-point observations of solar wind discontinuities'), it indicates that this DD is a tangential discontinuity.