Observations of Blue Corona Discharges in Thunderclouds

Abstract

<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>

Global Distribution of Key Features of Streamer Corona Discharges in Thunderclouds

“…The two groups of BLUEs with fast (≤50 μ s) and slow (>50 μ s and up to ∼0.8–1.0 ms) rise times are consistent with those mentioned in Husbjerg et al. (2022).…”

“…[2021] and Husbjerg et al. [2022]). These findings suggest that monitoring the occurrence and the features of BLUEs could serve as an indicator to characterize severe weather (deep convection episodes) (Husbjerg et al., 2022; Liu et al., 2018; Soler et al., 2021).…”

“…In particular, Husbjerg et al. (2022) show the difference in convection levels for lightning‐producing storms and BLUE‐producing storms.…”

“…A variety of BLUEs including kilometer‐scale blue discharges at the cloud top layer at ∼18 km altitude, blue starters and a pulsating blue jet propagating into the stratosphere were color photographed from the International Space Station (ISS) (Chanrion et al., 2017). BLUEs have also been recently observed by the nadir‐pointing MMIA onboard ASIM in the ISS since April 2018 (Husbjerg et al., 2022; Li et al., 2021; Neubert et al., 2021; Soler et al., 2020). However, it is a known issue that powerful NBEs are highly likely to be misclassified or simply missed by lightning locating systems (Zhu et al., 2022).…”

Transition in Optical and Radio Features During the Early Development of Negative Intracloud Leader

“…First, if a leader channel forms, the detected 337 nm radiation was suggested to be able to well depict the leader channels in the stratiform regions with low cloud tops (Montanyà et al., 2021). Second, many authors have reported electrical activities from the top of cloud due to streamers only (Dimitriadou et al., 2022; Edens, 2011; Husbjerg et al., 2022; Li et al., 2022; Liu et al., 2021; Soler et al., 2020, 2021). The negligible 777.4 nm optical radiance implies the absence of leader channel formation.…”