A triggered lightning flash containing both negative and positive strokes

We present measured current, luminosity, and electric and magnetic fields for a rocket‐triggered two‐stroke flash. The first stroke lowered negative charge to ground and the second stroke lowered positive charge via the same channel. A triggered positive stroke is a very rare event. The measured negative return stroke peak current was −11 kA and the positive +5 kA, with the total charge transfers being −1 C and +24 C, respectively. Electric field measurements at 120 to 520 m indicate that the negative and positive dart leader charge densities were approximately constant with height, −7.2 × 10−5 C m−1 and +5.5 × 10−5 C m−1, respectively. Magnetic field measurements indicate a negative leader current of −1.9 kA and a positive leader current of +400 A. Negative and positive dart‐leader speeds are estimated to be 2.7 × 107 m s−1 and 0.7 × 107 m s−1, respectively. Negative and positive return stroke speeds are estimated to be 1.6 × 108 and 0.92 × 108 m s−1, respectively.