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Streamers are a type of electrical discharge characterized by a filament of weakly ionized plasma propagating as an ionisation wave. A multitude of streamers may be launched, for instance, from lightning leader tips, where their optical emissions form a corona. They pre-ionize and condition the atmosphere ahead of a lightning leader, assisting its continued propagation (Ebert et al., 2010;Raizer, 1980). Flashes of light from thunderstorm clouds have been observed in the second positive band of Nitrogen (N 2 2P) at 337 nm (blue) with no emission in the main lightning leader lines of OI at 777.4 nm (red), suggesting they are made of streamer breakdown. They are observed in the upper regions of clouds, with some at the very top (

We report on observations of corona discharges at the uppermost region of clouds characterized by emissions in a blue band of nitrogen molecules at 337 nm, with little activity in the red band of lightning leaders at 777.4 nm. Past work suggests that they are generated in cloud tops reaching the tropopause and above. Here we explore their occurrence in two convective environments of the same storm: one is developing with clouds reaching above the tropopause, and one is collapsing with lower cloud tops. We focus on those discharges that form a distinct category with rise times below 20 μs, implying that they are at the very top of the clouds. The discharges are observed in both environments. The observations suggest that a range of storm environments may generate corona discharges and that they may be common in convective surges.

<p>Blue electric streamer discharges in the upper reaches of thunderclouds are observed as flashes in the second positive band of molecular nitrogen at 337.0 nm (blue) with faint emissions from atomic oxygen at 777.4 nm (red), a dominant line of lightning leaders. Using 2.5 years of measurements by the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS), we find that their rise time distribution suggests two distinct categories. One includes those with fast rise times less than 30 mus that are relatively unaffected by cloud scattering and emanate from within ~2 km of the cloud tops, and the other those with longer rise times that come from deeper within the clouds. Satellite measurements show that the clouds with blue discharges have an average cloud top temperature ~200 K compared to ~210 K for those of normal lightning, suggesting that blue discharges occur in clouds that reach near the tropopause. The average convective available potential energy (CAPE) determined from ERA5 reanalysis data is ~1550 J/kg for the shallow events and ~1290 J/kg for the deeper events, compared to ~1010 J/kg for regular lightning, suggesting that the discharges favour strong convective environments. This is further indicated by the geographical distribution of blue discharges which show that they occur mainly near mountain ridges or coastlines known for their strongly convective environments.</p>

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