The top panel shows solar wind magnetic field measurements. The middle panel shows the solar wind flow pressure. The solar wind data was obtained from the OMNI database and has been timeshifted 10 min to account for the propagation time from the bow shock to the ionosphere. The bottom panel shows the Kp-index. Horizontal colored lines have been added to indicate the minimum, middle and maximum values of the NOAA space weather scale for geomagnetic storms (Poppe 2000). The vertical black line in the middle indicates midnight.