Two different hard-radiation phenomena are known to originate from thunderclouds: terrestrial gamma-ray flashes (TGFs)¹ and gamma-ray glows². Both involve an avalanche of electrons accelerated to relativistic energies but are otherwise different. Glows are known to last for one to hundreds of seconds, have moderate intensities and originate from quasi-stationary thundercloud fields^2,3,4,5. TGFs exhibit high intensities and have characteristic durations of tens to hundreds of microseconds^6,7,8,9. TGFs often show a close association with an emission of strong radio signals^{10,11,12,13,14,15,16,17} and optical pulses^18,19,20,21, which indicates the involvement of lightning leaders in their generation. Here we report unique observations of a different phenomenon, which we call flickering gamma-ray flashes (FGFs). FGFs resemble the usual multi-pulse TGFs^22,23,24 but have more pulses and each pulse has a longer duration than ordinary TGFs. FGF durations span from 20 to 250 ms, which reaches the lower boundary of the gamma-ray glow duration. FGFs are radio and optically silent, which makes them distinct from normal TGFs. An FGF starts as an ordinary gamma-ray glow, then suddenly increases exponentially in intensity and turns into an unstable, ‘flickering’ mode with a sequence of pulses. FGFs could be the missing link between the gamma-ray glows and conventional TGFs, whose absence has been puzzling the atmospheric electricity community for two decades.

已知两种不同的硬辐射现象起源于雷云：地面伽马射线闪光 （TGF）¹ 和伽马射线辉光²。两者都涉及加速到相对论能量的电子雪崩，但在其他方面有所不同。已知辉光持续 1 到数百秒，强度适中，起源于准静止的雷云场^2,3,4,5。TGF 表现出高强度，具有数十到数百微秒的特征持续时间^6,7,8,9。TGF 通常与强无线电信号^{10、11、12、13、14、15、16、17} 和光脉冲^{18、19、20、21} 的发射密切相关，这表明闪电领导者参与了他们这一代。在这里，我们报告了对不同现象的独特观察结果，我们称之为闪烁伽马射线闪光 （FGF）。FGF 类似于通常的多脉冲 TGF^22、23、24，但具有更多的脉冲，并且每个脉冲的持续时间比普通 TGF 更长。FGF 持续时间从 20 到 250 毫秒不等，达到伽马射线辉光持续时间的下限。FGF 是无线电和光学静音的，这使它们与普通 TGF 不同。FGF 开始时是普通的伽马射线辉光，然后强度突然呈指数级增加，并变成不稳定的“闪烁”模式，并带有一系列脉冲。FGF 可能是伽马射线辉光和传统 TGF 之间缺失的一环，二十年来，传统 TGF 的缺失一直困扰着大气电力界。