Observations of Blue Corona Discharges in Thunderclouds

Blue electric streamer discharges in the upper reaches of thunderclouds are observed as flashes of 337.0 nm (blue) with faint or no emissions of 777.4 nm (red). Analyzing 3 years of measurements by the Atmosphere-Space Interactions Monitor on the International Space Station, we find that their distribution in rise time falls into two categories. One with fast rise times of 30 mu s or less that are relatively unaffected by cloud scattering and emanate from within similar to 2 km of the cloud tops, and another with longer rise times from deeper within the clouds. 50% of cells generating shallow events are associated with overshooting tops compared to 34% of cells generating deeper events. The median Convective Available Potential Energy of the cells is similar to 70% higher for the shallow events and similar to 38% higher for the deeper events than for lightning cells, suggesting the discharges are favored by strongly convective environments.