Abstract
AbstractThe maximum measured electric fields in thunderclouds are an order of magnitude less than the fields required for electric breakdown of the air. Several explanations for lightning initiation in these low‐intensity fields exist. One explanation is that electric breakdown first occurs at the surfaces of hydrometeors where the ambient field is enhanced very locally due to the drop geometry. Laboratory experiments have indicated that colliding raindrops which coalesce to form elongated water filaments, can produce positive corona in ambient fields close to those measured in thunderclouds. We calculate the electric field distribution around a simulated coalesced drop, and use a numerical model to study the positive‐corona mechanisms in detail. Our results give good agreement with the laboratory observations. At the altitudes and reduced pressures at which lightning initiation is observed, our results show that positive corona can occur at observed in‐cloud electric fields strengths.
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