Figures for Flight 747:

(a) The side view shows the vertical Ez field component along the airplane's path. The labels a, b, c, d, etc., are used just to mark the time or position for convenience. For example, point c corresponds to 23.98 UTC which ca be related to a point of the airplane track at the same time. From point (or time) b to c, the Ez field is strong and negative, indicating positive charge above the airplane or negative charge below the airplane.

(b) The particle charge panel shows when and how many charged particles are encountered and how large is the charge on a particle along the path (or time) of the airplane. For example, it is only near time labeled "a" (about 23.8 UTC) the airplane begins to measure some charged particles. In the middle, between b and c, large magnitude of both positively and negatively charged particles are measured.

(c) The net charge panel shows the net charge density along the airplane’s path. It is calculated by evenly dividing the total path into 5 seconds segments; then adding all the charged particle's charge together and dividing the sum by the sample volume of the HVPS charge sensor. Each point shows the averaged charge density in that 5 seconds segment. At the times 23.9 and 24.1 UTC, the data shows that the airplane goes into a net negative charge region first and then goes into a net positive charge region, but when comparing the same time intervals in the individual particle charge data, in the net negative charge region or the net positive charge region, the positively and negatively charged particles co-exist.