Observation of Blue Corona Discharges and Cloud Microphysics in the Top of Thunderstorm Cells in Cyclone Fani.

Blue corona discharges are often observed at the top of thunderclouds. They are bursts of streamers, but the cloud conditions that enable them are not well known. Here we present observations by the Atmosphere‐Space Interactions Monitor (ASIM) of 92 discharges during its ∼1 min pass over tropical cyclone Fani in the Bay of Bengal from 20:10:55 to 20:12:05 UTC on 30 April 2019. The discharges were observed in convective cells forming in the rainbands of the cyclone where Convective Available Potential Energy reached ∼6,000 J kg−1. The Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite passed over one of the cells ∼12 min after ASIM from 20:23:58 to 20:24:14 UTC. It measured the cloud microphysics related to the discharges and indicated they occurred in a convection region with the cloud top overshooting for over 20 min. The updraft lifted ice particles to lower stratospheric altitudes and formed the gullwing‐shaped cirrus. The discharges are found at an average altitude of ∼16 km where the cloud environment contained ∼2 × 107 m−3 ice particles with ∼50 µm radius, resulting in a photon mean free path of ∼3 m. Around 20% of the blue corona discharges coincide with Narrow Bipolar Events indentified from the Earth Networks Total Lightning Network. Our observations suggest that the overshooting cloud top formed by deep convection and a surge in lightning activity facilitated conditions for the blue corona discharges. This work provides the first‐ever estimate of important microphysical parameters related to blue corona discharges based on data measurements, establishing a reference for future empirical and theoretical studies. Plain Language Summary: Blue corona discharges are bursts of streamer discharges often observed at the top of thunderclouds, but the conditions in the clouds that generate them are not well understood. In this study, we discuss observations of blue corona discharges in convective cells detected by the Atmosphere‐Space Interactions Monitor on the International Space Station as it passed over cyclone Fani in the Bay of Bengal. For the first time, we have observations of the cloud particle characteristics at the cloud tops taken shortly afterward by the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite, which are related to the blue corona discharges. The observations indicate that the blue corona discharges may be Narrow Bipolar Events associated with strong convection in cloud cells reaching into the stratosphere. The cloud microphysical parameters related to blue corona discharges are important for future empirical studies and for theoretical models and simulations. Key Points: First combined observations of optical activity, cloud microphysics and lightning related to blue corona discharges in a tropical cycloneThe source depth of the blue corona discharges inside the cloud estimated from optical and radio observations agree wellBlue corona discharges are related to a strong updraft, high‐density large ice particles and an increase in the total lightning rate [ABSTRACT FROM AUTHOR]