USTC: Researchers Reveal the Optical Features of Cloud Top Discharges

Recently, the research team led by Prof. LEI Jiuhou, Prof. ZHU Baoyou and Prof. LU Gaopeng from the University of Science and Technology of China (USTC) revealed, for the first time, the optical features of cloud-top discharges and its perturbations on the lower ionosphere. They proposed a new approach to detecting the cloud-top thunderstorm discharges and studying the coupling of the middle and upper atmosphere.



This work was published in Nature Communications with the title “Optical emissions associated with narrow bipolar events from thunderstorm clouds penetrating into the stratosphere”.



The lightning in the tropopause can induce the magnificent phenomenon of discharges in the middle and upper atmosphere. According to the onset height of lightning, the discharges can be divided into cloud-top type (blue jets and gigantic jets) and lower ionosphere type (halos and (sprites) elves).



Narrow bipolar events (NBEs) are a distinct class of cloud top discharges produced in the deep convection thundercloud penetrating the stratosphere, which has been suggested to trigger blue emissions.



However, due to the lack of observation with the high spatial and temporal resolution, the luminous features of NBEs remain a mystery and under debate.



For this purpose, the research team proposed a new method to remote sense the cloud top discharge by measuring its associated radio signals based on the self-developed lightning array.



By using the sferic array and the Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station, the researchers analyzed a strong thunderstorm in Southern China occurred in August 2019. They observed, for the first time, that negative NBEs were always associated with blue emissions at 337 nm, while not with emissions at 777.4 nm like normal lightning.



Moreover, by analyzing the negative NBE signals and its accompanying blue spectral signals, the researchers also found that the peak current of NBEs was closely correlated with the spectral signal of blue emissions.



The findings on the distinct optical feature of NBEs rectified the traditional point that NBEs were non-luminous and provided new insights to distinguish lightning types and monitor strong convection from space.




“This is a good paper which reports new results addressing a long-standing puzzle in lightning science. The observations of emissions from the tops of thunderclouds is not only impressive but is also tremendously important for the research,” the reviewer commented.

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