Analysis of blue discharges detected by ASIM-MMIA with indication of their source altitudes and electromagnetic signatures
Abstract
The Atmospheric Space Interaction Monitor (ASIM) was successfully launched last April 2, 2018 to study lightning, transient luminous events (TLEs) in the atmosphere above thunderstorms, and Terrestrial Gamma-ray Flashes (TGFs). In this work, we present preliminary analysis of transient blue discharges reported by the Modular Multispectral Imaging Array (MMIA) of the ASIM payload. These blue discharges are only detected by the 337 nm filtered ASIM-MMIA photometer and camera and with no traces of the 777 nm emission typical of lightning.
We analyze 30 blue events produced in a strong thunderstorm that occurred over Indonesia on May 14, 2019. We show some features of these optical events, such as characteristic time, position, illuminated cloud top area and peak brightness. We also analyze the VLF electromagnetic signatures of these events recorded by the ground-based Melaka of the Lightning Effect Research Platform (LERP) in China. According to our results, there are two different types of blue discharges in the observed thunderstorm. Out of the 30 events, 10 were narrow single pulse events that last between 1.6 and 3.6 ms. The rest are multiple pulse blue events, lasting over 17 ms. The detected blue flashes are organized in a spatial and temporal cluster located in the middle of an intense thunderstorm in which the cloud top height (CTH) reaches above 17 km as reported by the China's second-generation geostationary meteorological FY-4A satellite covering China and surrounding areas. The analysis of the process of scattering and absorption of the emitted 337 nm photons through the thunderclouds has allowed us to derive a distribution that fits the single-pulse blue event photometric signals. From the fit we have determined the blue events source altitudes that range between 1.7 km and 6.5 km below the thundercloud top. Thus, we have found that the blue flashes detected by ASIM emanate from sources located between > 10 km and > 15 km altitude (inside the cloud), consistent with the altitude of simultaneous positive narrow bipolar events (+NBE) reported by LERP.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMAE23A..02P
- Keywords:
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- 3304 Atmospheric electricity;
- ATMOSPHERIC PROCESSES;
- 3324 Lightning;
- ATMOSPHERIC PROCESSES;
- 3394 Instruments and techniques;
- ATMOSPHERIC PROCESSES