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We report here three‐point measurements of bursty, velocity‐dispersed, field‐aligned electron precipitation at the poleward edge of a northward‐moving, post‐breakup, nightside auroral arc. The three‐point measurement allows detection of the proper motion of the inverted‐V arc, which is shown to be 550 m/sec northward. The velocity dispersion patterns are fitted to find the source altitude of the precipitation bursts as a function of distance from the poleward edge of the arc. These source points are interpreted to trace out the low‐altitude boundary of the inverted‐V potential drop, which is seen to rise both in time, and in the northward direction. The precipitation bursts under the inverted‐V are seen to have an arc‐aligned velocity which varies with time, and which is consistent with the measured E × B local drift speed.

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