Multiple‐Stroke Positive Cloud‐to‐Ground Lightning Observed by the FALMA in Winter Thunderstorms in Japan

Abstract

AbstractMultiple‐stroke (MS) positive cloud‐to‐ground (+CG) lightning flashes are rarely reported, especially those with high‐quality location information. In this study, we report 47 MS +CG flashes observed in winter thunderstorms in Japan with a 14‐site fast antenna lightning mapping array (FALMA). MS +CG flashes account for 18% of +CG flashes. The mean multiplicity of all +CG flashes is 1.24, and the maximum multiplicity is 5. Interstroke intervals have a very large range from 1.0 to 1,320.6 ms with the geometric mean of 64.4 ms. In three flashes, interstroke intervals smaller than 2 ms are observed, and corresponding positive strokes are inferred to be produced by two branches of the same positive leader. Horizontal distances between sequential positive strokes range from 1.1 to 37.3 km with the geometric mean of 9.7 km. No subsequent strokes struck at the same location as a previous stroke. Distances between sequential strokes are generally much larger than distances between first strokes and lightning initiation locations. Subsequent stroke peak amplitudes are on average 0.45 of first stroke peak amplitudes. In 39 flashes (83%), the first stroke is stronger than the largest subsequent stroke in the same flash. Subsequent stroke amplitudes are weakly correlated with the time difference from the previous stroke. Origination mechanisms of positive leaders initiating first and subsequent positive strokes are discussed. It is very likely that positive leaders for most subsequent strokes originate from in‐cloud negative leader channels, but origination mechanisms for positive leaders initiating first strokes are more varied.