Figures for Flight 748:

(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 a time about 22:25 UTC which can be related to a point of the airplane track at the same time. From point (or time) b to c, the Ez field changed its sign frequently, indicating frequent lightning discharges, which alters the charge distribution above or 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 near time 22:17 UTC that a larger magnitude of charge is found to be on the particles. In the same region along the airplane's path, both large 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. From 22:17 to 22:22 UTC, the data shows that the airplane goes into a net negative charge region first and then goes into some net positive or net negative charge regions, though positively and negatively charged particles co-exist in the same 5 seconds segments.

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