基于TEROS的自然闪电X射线暴观测研究

本文报道了国内首个自然闪电高能辐射(Lightning Energetic Radiation, LER)多点观测结果. 基于自主研发的雷暴高能辐射观测系统(Thunderstorm Energetic Radiation Observation System, TEROS), 在2021年夏季观测期成功捕获3次自然LER事件, 结合闪电定位、低频快电场变化、回击峰值电流等其他资料, 对3次事件的高能辐射特征进行研究. 分析发现: 3次LER事件均于负地闪下行先导的最后阶段被探测到, 是典型的X射线暴, 且均具有MeV能量的单光子, 最大能量超过2.2 MeV; 伴随梯级先导出现的X射线暴持续时间为数百μs, 伴随不规则直窜先导的X射线暴持续时间为数十μs, 主要与先导发展速度有关; 相应回击峰值电流最大的1次事件具有最高的单光子能量、最大的单位面积沉积总能量和最多的爆发过程数量, 随着接近回击时刻, 该事件还表现出与电场变化一致的增强趋势, 表明先导头部电场是影响高能辐射产生的重要因素; 随到达强度降低, 高能辐射信号逐渐由束流模式向单光子模式转变, 呈现出与地球伽马射线闪类似的现象学特征, 更多乃至所有的爆发过程无法被探测到, 高能辐射可能是闪电发展过程中的普遍现象.

Observations of X-ray bursts from natural lightning flashes by TEROS

This work presents the first multi-point observations of natural Lightning Energetic Radiation (LER) in China. In summer of 2021, 3 LER events were recorded by the independently-developed Thunderstorm Energetic Radiation Observation System (TEROS). Combining with the lightning location data, low-frequency fast electric field change waveforms and return stroke peak currents, the energetic radiation characteristics of the 3 events are investigated in detail. All of the 3 LER events were detected during the last stages of the downward leaders before the negative cloud-to-ground lighting return strokes, which were typical X-ray bursts having photons with energy of MeV, and the maximum energy exceeded 2.2 MeV. The durations of the 2 X-ray bursts accompanying the stepped leaders were hundreds of microseconds, while the duration of the other one accompanying the chaotic dart leader was tens of microseconds, which can be attributed to the difference of the developing speeds of various types of leaders. The X-ray burst with the largest return stroke peak current had the highest single photon energy, the largest total deposited energy per unit area and the largest number of burst process. While approaching the return stroke, the intensity of this event also showed an increasing trend consistent with the electric field change, indicating that the electric field at the leader tip is an important factor affecting the production of energetic radiation. With the decrease of the arrival intensity, the energetic radiation signals gradually changed from the beam mode to the single photon mode, showing the phenomenological characteristics similar to Terrestrial Gamma-ray Flashes (TGFs), and more or even all of the burst processes could not be detected. We suggest that energetic radiation may be a common phenomenon during the development of lightning.