Figures for Flight 751:

(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 24.18 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 changes its magnitude and sign, indicating the variation of charge distribution in the cloud.

(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, at about 24.02 UTC, the airplane measured a mixture of positive and negative charged particles. The charge magnitude is large on some of individual particles.

(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 for each segment add all charged particle's charge together and divide the sum by the sample volume of the HVPS charge sensor. Each point shows the averaged charge density in that 5 seconds segment. At 24:00 UTC, the data shows that the airplane mainly goes into some positive charge regions.

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