| Autor: |
Lyu, Fanchao, Qin, Zilong, Cummer, Steven A., Zheng, Yu, Jiang, Sulin, Zheng, Tianxue, Liu, Yan, Xu, Wei, Lyu, Weitao |
| Předmět: |
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| Zdroj: |
Geophysical Research Letters; 10/28/2024, Vol. 51 Issue 20, p1-10, 10p |
| Abstrakt: |
Upward Terrestrial Gamma‐Ray Flashes (TGFs) are mainly produced during the upward propagating negative leaders inside thunderclouds. The exact source position of TGFs, which is crucial to understanding TGF source properties, is still unclear. The link between positive energetic in‐cloud pulses (+EIPs) and TGFs provides us with a potential target to aim at. In this study, the low‐frequency radio emissions of 75 +EIPs are analyzed to retrieve the source altitudes with an improved ray theory model. Furthermore, the meteorology contexts of +EIPs derived from the ground‐based weather radars and satellite‐based infrared cloud top temperature measurements are investigated. +EIPs are produced at 8.8–13.7 km, with an average of 11.3 km inside thunderclouds, and at an average of ∼2.5 km below cloud tops. These altitudes indicate that a total number of 1.7 × 1016 to 2.6 × 1018 gamma ray photons with energy greater than 1 MeV are required for an EIP‐TGF to be measured by spaceborne detectors. Plain Language Summary: Terrestrial gamma‐ray flashes (TGFs) are high‐energy photon emissions generated during thunderstorms and related to the initial development of intra‐cloud discharges. How TGFs are produced inside thunderclouds is still an open question, and one crucial issue is where TGFs are produced. Till now, it has been challenging to obtain the TGF positions directly. Recently, a distinct type of high‐peak current events, which are named energetic in‐cloud pulses (EIPs), are found to be closely linked to TGFs. The radio emissions of EIPs can be measured by ground‐based radio sensors deployed hundreds of kilometers away from the source. In this study, a ray theory model is improved to retrieve the signature of very low‐frequency/low‐frequency radio signals of EIPs propagating in the Earth‐ionosphere waveguide to obtain the source altitudes of EIPs. A total of 75 EIPs were found to be produced at 8.8–13.7 km, with an average of 11.3 km inside thunderclouds, and at an average of ∼2.5 km below cloud tops. With the source position information and combining the previously reported method to estimate the total number of source electrons, we suggest a total number of about 1017 is needed for TGFs being detected by spaceborne gamma ray detectors. Key Points: An improved ray theory model is developed to retrieve energetic in‐cloud pulse (EIP) positionsSeventy‐five +EIPs are located at 8.8–13.7 km, with a mean altitude of 11.3 kmA mean gap of ∼2.5 km between EIPs and cloud tops was estimated [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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