Abstract
AbstractNarrow Bipolar Events (NBEs) are powerful radio emissions from thunderstorms, which have been recently associated with blue optical flashes on cloud tops and attributed to extensive streamer electrical discharges named fast breakdown. Combining data obtained from a thunderstorm over South China by the space‐based Atmosphere Space Interactions Monitor, the Vaisala GLD360 global lightning network and very low frequency/low frequency radio detectors, here we report and analyze for the first time the optical emissions of blue luminous events associated with negative NBEs and located at the top edge of a thundercloud. These emissions are weakly affected by scattering from cloud droplets, allowing us to estimate the source extension and optical energy involved in the process. The optical energy in the 337‐nm band emitted by fast breakdown is about 104 J, which involves around 109 streamer initiation events.
Highlights
Combining data obtained from a thunderstorm over South China by the space-based Atmosphere Space Interactions Monitor, the Vaisala GLD360 global lightning network and very low frequency/low frequency radio detectors, here we report and analyze for the first time the optical emissions of blue luminous events associated with negative Narrow Bipolar Events (NBEs) and located at the top edge of a thundercloud
Blue luminous events, such as blue jets and blue starters, are transient electrical phenomena that occur in active thunderstorms and are characterized by optical signals strongly dominated by the blue range of the spectrum and lasting from about one millisecond to hundreds of milliseconds
The eight Blue Luminous Events (BLUEs) events that we analyze in this study expand and complete the picture of fast breakdown as the source of both optical blue-dominated emissions and radio pulses detected as NBEs in the very low frequency (VLF)/low frequency (LF) bands or high-amplitude noise in VHF
Summary
Blue luminous events (hereafter, BLUEs), such as blue jets and blue starters, are transient electrical phenomena that occur in active thunderstorms and are characterized by optical signals strongly dominated by the blue range of the spectrum and lasting from about one millisecond to hundreds of milliseconds. The blue color indicates the presence of electron-impact excitation of molecular nitrogen (Gordillo-Vázquez & Pérez-Invernón, 2021; Pasko, 2008; Surkov & Hayakawa, 2020) and the weak or absent atomic oxygen line at 777.4 nm, indicates that air does not reach high temperatures, typically associated with lightning leaders at ground level This points to streamer coronas being the key component of BLUEs, a conclusion supported by the close association between BLUEs and narrow bipolar events (NBEs) Soler et al (2020) analyzed a set of 10 BLUEs associated with positive NBEs and at a considerable depth inside the cloud, presumably between the main negative and the upper positive charge region of the cloud As these events are deeply buried in the cloud, the scattering by cloud droplets and ice crystals blurs their image as observed from above, resulting in a diffuse blob that can be identified with the blue glimpses reported by Chanrion et al (2017). This allows us to compare to radio observations of fast breakdown
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