闪电是怎么产生的？答案越来越有趣了。
内容总结：
最新研究发现：闪电形成机制远比想象复杂
长期以来，闪电被视为云层中电荷积累到临界值后产生的巨大电火花，但最新研究揭示，这一自然现象背后隐藏着更为复杂的物理过程，涉及高能粒子、宇宙射线甚至超新星爆发等极端天体事件。
传统理论遭遇挑战
18世纪以来，科学家普遍认为闪电原理与实验室中的电火花类似：当云层中电场强度达到每米约300万伏特的临界值时，空气被击穿，形成放电通道。然而20世纪中期的实地观测发现，雷暴云的实际电场强度通常仅为临界值的十分之一，最强也仅达到三分之一。这一矛盾长期困扰着气象物理学家。
高能粒子理论兴起
上世纪90年代，卫星在雷暴云中意外探测到伽马射线——这种通常出现在超新星爆发或中子星碰撞中的高能辐射。这一发现促使科学家重新审视闪电机制。新罕布什尔大学物理学家约瑟夫·德怀尔提出，当电子以接近光速运动时，可以产生"逃逸雪崩"效应：高速电子撞击空气分子释放更多电子，形成链式反应，同时释放伽马射线。这一过程可能在云层中不断叠加，最终触发闪电。
最新观测提供证据
2023年7月，美国国家航空航天局（NASA）的ALOFT研究项目派遣高空飞机飞越墨西哥湾、加勒比海等地强风暴核心区域，携带伽马射线探测器进行观测。结果显示，雷暴云中存在大量此前未被发现的伽马射线活动，包括持续辉光和突发闪光，甚至在没有可见闪电时也会产生。这一发现与德怀尔的理论预测高度吻合，成为目前支持高能粒子理论的最有力证据。
新的谜团：宇宙射线假说
今年初，洛斯阿拉莫斯国家实验室的研究人员通过分析闪电起始阶段的无线电波传播方向发现，早期电流移动方向与电场方向存在微小偏差。这一现象暗示，闪电可能并非单纯由云内电场驱动，而受到来自外太空的高能宇宙射线影响。这些宇宙射线是遥远星系中超新星爆发或黑洞吞噬物质时喷射出的质子、铁原子等粒子碎片，它们穿越亿万光年后撞击地球大气层，产生的高速电子簇可能成为点燃闪电的"火种"。
研究前景
目前科学家认为，闪电触发机制可能并非单一：冰晶针状结构、高能电子雪崩、宇宙射线等多种因素可能协同作用，在不同云层条件下各自扮演关键角色。德怀尔感叹："每次深入研究，都发现闪电比我们想象的更离奇。我们现有的简单模型显然远未完整。"随着观测技术的进步，这一经典自然现象背后的物理学图景正在被不断改写。
中文翻译：
闪电的成因是什么？答案正变得越来越有趣。
引言
在改变我们对地球闪电的认知之前，约瑟夫·德怀尔曾在更为宇宙化的场景中研究天气。借助美国国家航空航天局（NASA）距离百万英里轨道上的“风”卫星传感器，他观测太阳喷射出的耀斑，分析从太阳表面流出的粒子流。然而，在千禧年前后搬至佛罗里达时，德怀尔觉得准备好探索新事物——一些他和学生们可以自主研究的问题。不久，热带天气就在他办公室窗外送来一个适逢其会的谜团。“外面就像‘轰、轰、轰’一样，”德怀尔说，“我仔细一看，意识到闪电是一个未解之谜。”
雷暴已令人类着迷数千年之久，然而其内部机制至今仍深藏奥秘。雷云是不透明的，靠近它们非常危险，而且它们体积太大，无法装进实验室。近三个世纪以来，好奇的研究者一直将风筝、气球和火箭送入雷云，也学到了很多知识。但每当闪电爱好者接近这一现象时，他们就会发现认知中存在巨大空白。在过去50年里，研究者尤其聚焦于一个空白：那道锯齿状、白热空气构成的通道——我们称之为闪电——究竟是如何形成的？
近年来，这一领域经历了一场复兴，研究者——其中许多是像德怀尔一样转行研究天体物理的人——设计出了穿透云层的新方法。他们拿来了大量原本用于研究剧烈宇宙事件的仪器，并将其对准了地球雷暴的狂暴景象。他们看到闪电在蜿蜒行进时射出X射线，在雷云中探测到闪烁的伽马射线光芒，并且就在不久前，还发现了闪电向意想不到方向行进的迹象。
没有人能将所有碎片拼合起来，但一种关于闪电的新认知正在成形。那些令人畏惧的闪光，越来越不像物理学家们曾经所设想的巨型电火花。虽然电学起着核心作用，但闪电的形成和塑造却需要从宇宙爆发到粒子物理等整个物理学范畴。特别是，触发一道闪电似乎需要极端事件——这些事件通常与超新星、黑洞和粒子对撞机有关，而与松软的云朵相去甚远。
“这一领域正逐渐形成共识：高能过程在闪电引发中扮演着关键角色，”新墨西哥理工大学大气物理学家凯塔诺·达席尔瓦说，“现在进入这个领域是一个激动人心的时刻。”
触发点
当闪电划破天际时，古希腊人、斯堪的纳维亚人和印度教信徒看到的是神灵的战争闪光。当雷声震得人胸口发麻时，中国人则认为是神灵在惩罚作恶者。如今，雷暴的力量依然令人心生敬畏。
“在巴西，我从小看着这些带着大量闪电的巨大冷锋来临，”达席尔瓦说，“我对此感到恐惧。”
恐惧伴随而来的是着迷。然而，尽管经过了几个世纪的探索，像达席尔瓦这样着迷的物理学家依然在追问古人同样的问题：闪电是如何开始的？
曾经有一段时间，研究者以为他们找到了答案。随着18和19世纪物理学家们揭开了电的神秘面纱，他们学会了如何按指令产生可观的电火花：在一个金属球上聚积电荷，将第二个金属球靠近，火花便在两者间跳跃。当研究者最终弄清了物质的结构时，他们理解了其原因。分离的电荷在两球之间产生了一个电场。当电场达到临界强度——大约每米300万伏特——空气便开始被瓦解。电场将自由的电子投入邻近的原子中，在那里它们又撞出更多的自由电子。就像陡峭山坡上的雪崩一样，电子发生“雪崩”，使空气升温直至发光。
本杰明·富兰克林在1752年著名的风筝实验中，将实验室里的火花与天空中的闪电联系了起来。在接下来的200年里，研究者相信，雷云中所发生的与金属球之间所发生的完全一样，只是规模更大而已。闪电之谜似乎已经被解开。
但到了20世纪中期，当物理学家从风筝升级到火箭和卡车大小的探空气球时，他们发现了一个问题。云层中确实存在电场；微小的冰晶像袜子在地毯上摩擦一样互相摩擦，而多出电子的冰晶往往会堆积在云层底部。但这些电场非常微弱。典型的雷暴所具有的电场能量仅为产生火花所需能量的十分之一，而迄今为止测到的最强电场也只达到了临界强度的三分之一。然而，根据NASA的卫星数据，全球在任何时刻都有超过2000场雷暴在发生——这个观测结果就像“初学者坡道上发生雪崩”一样令人费解。
“你得把电场一直增强到超过常规击穿阈值才行，”俄克拉荷马大学恶劣与高影响天气研究与运行合作研究所的研究员迈克尔·斯托克说，“但在自然界中，这似乎并不会发生。”
一道可见的闪电意味着空气已经被分解成一堆炽热、带电的亚原子碎片。因此，要么是某种因素极大地增强了电场，使其超过临界阈值，要么就必然是其他某种过程在分解空气分子。问题是：那是什么？
另一个线索再次来自富兰克林。他观察到，尖锐的尖端更可能引发或接收火花。物理学家现在明白，这是因为尖锐的导体会增强附近的电场。在20世纪60和70年代，佛罗里达和法国的物理学家开始通过向雷云发射带有尖端的微型火箭来人为触发闪电。火箭后面会放出一条导线，引导闪电到达地面。
大多数雷云并没有安装火箭的飞镖来帮助它们产生火花，但它们确实有冰晶，其中一些冰晶可以超过铅笔橡皮擦的大小。这些冰块也是导体，并且可能伸展成碎片状。物理学家估计，足够长的冰碎片可以将场强提高10倍或更多，而多个所谓的“水凝物”协同作用效果更佳。似乎，这个谜题又解开了。
然后物理学家开始从太空观测风暴，并了解到雷云比他们想象的要奇怪得多。
逃逸雪崩
1994年，一颗搜寻极端深空爆发的卫星偶然捕捉到雷云中发出的伽马射线闪光，这些闪光常常伴随着闪电出现。伽马射线是能量最高的光线类型，通常标志着垂死恒星的最后喘息或两颗中子星相撞的灾难性巨响。无论云层中含有多少尖锐的冰屑，都不应该期待从中产生伽马射线。在快速剧烈的亚原子粒子领域，有些不同寻常的事情正在发生。
大约就在这个时候，德怀尔目睹了佛罗里达轰鸣的雷暴，并了解到了它们神秘的起源。作为一名天体物理学家，他了解亚原子领域。他熟悉诺贝尔奖得主C.T.R.威尔逊的研究成果，后者曾假设一个以接近光速运动的“相对论性”电子几乎不会感受到空气中原子的阻力（达席尔瓦将其比作子弹撕裂一场雪花纷飞）。因此，一个在电场中运动速度足够快的电子可以“逃逸”并越来越快。
德怀尔知道，俄罗斯物理学家亚历山大·古列维奇在1992年曾证明，这样一个逃逸电子可能引发可能多达10万电子的级联，类似于实验室中引发火花的雪崩，但过程中尺度可达几百到几千米。他还知道，当这些相对论性逃逸电子撞击空气分子时，它们可以发射伽马射线。
单靠这些极端的亚原子事件，似乎不足以产生照亮雷云的明亮伽马射线。但随后，德怀尔设想了一个复杂的过程，使得一次雪崩可以触发另一次雪崩，再触发另一次，一次又一次，全都紧密叠在一起。
根据德怀尔的过程，当雪崩中的一个电子与一个原子碰撞时，电子可能发生反弹并发射出一个伽马射线光子。这个伽马射线光子会转变为一个电子及其反物质孪生兄弟——正电子。云层中的电场会将这个正电子向后推，接近雪崩开始的地方。在那里，它可能撞上另一个原子，引发另一次雪崩，从而产生更多伽马射线、更多正电子、更多雪崩，如此循环，直到产生一道从轨道上都可见的闪光。
“这就像把一个麦克风贴在扬声器旁边，”目前在纽汉普郡大学的德怀尔说，“声音很快就会变得非常大。”
这种相对论性逃逸雪崩的叠加可以解释伽马射线的来源。它也可能有助于闪电的引发。随着雪崩级联扩展，电子在阵面堆积，同时在它们身后留下带正电的离子——从而增强云层中的电场。
在计算机模拟中，德怀尔展示了这一系列事件放大了雪崩、辐射出伽马射线，并增强了电场。大约在同一时间，对冰碎片的详细模拟揭示了它们可能达到的尖锐程度——并不非常尖锐——这也开始削弱了水凝物理论。
那么，德怀尔的相对论性逃逸雪崩真的在云层内部发生吗？这能否将电场增强到足以产生闪电的程度？他的同事意见不一。
研究者需要更接近这一现象。2023年7月，一些大胆的物理学家给一架NASA高空飞机配备了伽马射线探测器，并将其直接飞越了地球上一些最猛烈风暴的核心——墨西哥湾、加勒比海和中美洲的热带风暴。这架飞机到达了“大多数人会不惜一切代价避开”的平流层高度，达席尔瓦说。这项行动名为“ALOFT”（其名称部分来自其他缩写的首字母组合）。它的观测带来了整整一代人中最大规模的新数据富矿。
ALOFT揭示，雷云就像沸腾的坩埚，发射着各式各样从太空难以看到的伽马射线。该项目确认了太空设备也曾探测到的闪电周围的微弱辉光和突然闪光。但ALOFT还发现，即使没有可见的闪电，云层也会闪光。最奇特的是，它们还会闪烁。
“他们发现存在着一整套其他现象，”荷兰埃因霍温理工大学的闪电物理学家乌特·埃伯特说。
有一个人对ALOFT的观测结果并不感到完全意外，那就是德怀尔。在ALOFT团队公布结果之前，他重新运行了自己的模拟，以预测飞越风暴时他们的伽马射线探测器会看到什么。他早就知道，相对论性雪崩必然会以闪烁的模式堆积，因此他精确计算出了粒子碰撞会产生何种闪烁。两支团队都在2023年12月旧金山举行的美国地球物理联合会年会上展示了他们的发现，结果完全吻合——这是迄今最强有力的证据，表明德怀尔的亚原子碰撞确实在真实的雷暴中发生。
现在，其他理论家正在此理论上进行构建。去年夏天，宾夕法尼亚州立大学的电气工程师维克托·帕斯科研究了在其他条件（如更高电场）下触发的连锁事件，并发现即使在这些情况下，雪崩也能够堆积并引发闪电，这为整个框架提供了额外的支持。
“这巩固了‘高能电子在此发挥作用’的观点，”达席尔瓦说，“直到最近，实际上只有德怀尔在谈论这个。”
与电场不一致
高能电子雪崩链很可能正在使云层发光、闪烁并产生伽马射线闪光。但研究者无法肯定正是它们引发了闪电。一个难题是，闪电似乎从云层中的一个点开始，而雪崩则发生在一个大得多的区域。雪崩使云层接近预期会导致闪电的条件。但没有人将它们与闪电的触发完全联系起来。
即使德怀尔的理论获得了支持，2025年初的观测结果又复兴了另一种关于闪电生成的理论。
在新墨西哥州的沙漠中，两个布满天线的站台捕捉到了十几次独立闪电发出的无线电波。利用这些数据，洛斯阿拉莫斯国家实验室的研究员邵轩民得以重建了这些闪电起始期间整体电流的流动方式。他发现有些不对劲。如果是德怀尔级联中的某一种，或任何其他纯粹由电场驱动的过程在孕育闪电，那么原始闪电从过程一开始就会与电场方向完美对齐。但邵发现，在这些案例中，这两个方向略有偏差。在这种倾斜中，邵看到了闪电起源于地球之外、甚至银河系之外的证据——一种宇宙射线簇射。
宇宙射线簇射是深空剧烈事件的最终结果，比如吸积黑洞喷射出的粒子，或者恒星爆炸释放出原子碎片——可能来自爆炸恒星的一个质子，或是超大质量黑洞喷射出的一个剥去电子的铁原子。这些碎片穿越数十亿光年的宇宙，撞击地球大气层。剧烈的碰撞会喷射出一股电子、正电子和其他粒子，以随机角度倾泻进入云层。这些电子和正电子可能具有足够的能量，将电子从分子上分离并启动雪崩，即使电场远低于临界阈值。
对于一些物理学家来说，邵的论点很有说服力。“这必定是映射了其他东西的方向，最有可能的是宇宙射线电离，”加州大学圣克鲁兹分校的物理学家大卫·史密斯说，“我觉得这些数据非常有说服力。”
其他人则表示，现在就下结论还为时过早。邵的重建技术尚未完全确立，而宇宙射线簇射中包含许多尚不明确的粒子物理过程。这使得人们很容易将其当作“魔法棒”，荷兰射电天文学研究所的物理学家布莱恩·黑尔说，用来填补一个神秘过程中原本难以解释的空白。
但如果邵和其他人开始看到更多闪电斜向飞行的实例，可能会激励理论家们去阐明这些细节。
“这是一个非常酷的想法，而且有迹象表明这种情况可能正在发生，”德怀尔说，“如果这个机制是真的，那么每当你看到一道闪电，它就与银河系中某处的一颗垂死恒星存在着物理联系。”
过去几十年的闪电研究提出了若干种关于自然界如何从电场微弱的云层中诱导出闪电的概念。虽然这些理论在科学文献中相互竞争，但在现实世界中它们很可能是协同合作的。细长的冰晶可能在一个云层中触发闪电，而同时产生伽马射线的电子洪流则在另一个云层中做到。多种机制也可能共同作用，将电场推过不可逆转的临界点。只有对伴随闪电而来的伽马射线和无线电波进行更精确的测量，研究者才有望确定哪一种机制（或哪一种机制组合）最为常见。
但是，正当物理学家们接近揭开闪电引发之谜时，他们再次发现了不符合任何理论的意外现象。例如，ALOFT观测到的伽马射线中存在细微的规律。而过去几年里，荷兰的一个射电望远镜阵列提供了迄今最清晰的闪电自起点开始分叉的图像。它们显示，一些部分快速射出，一些部分移动相对缓慢，还有一些在行进过程中会萌生出针状分支。
这些特征表明，即使解释越来越全面，关于闪电究竟如何运作的案例仍将被不断重新审视。“我们看得越多，它就变得越奇异，”德怀尔说，“显然，我们这里那些非常简单的图像真的是不完整的。”
英文来源：
What Causes Lightning? The Answer Keeps Getting More Interesting.
Introduction
Before he changed the way we understand lightning on Earth, Joseph Dwyer studied the weather in more cosmic settings. Using the sensors on NASA’s Wind satellite, orbiting a million miles away, he watched flares shoot out from the sun and analyzed the particles that stream from the sun’s surface. But when he relocated to Florida around the turn of the millennium, Dwyer felt ready for something new — something he and his students could investigate on their own. It didn’t take long before the tropical weather delivered a suitable mystery outside his office window. “It was like boom, boom, boom outside,” Dwyer said. “I looked into it and realized lightning was an unsolved problem.”
Thunderstorms have captivated humanity for millennia, and yet their inner workings remain deeply mysterious. Storm clouds are opaque. They’re dangerous to approach. And they’re too big to fit in a lab. Inquisitive researchers have been sending kites, balloons, and rockets up into them for nearly three centuries, and they’ve learned a lot. But every time lightning lovers get closer to the action, they discover major gaps in their understanding. For the past 50 years, researchers have focused on one particular gap: How does the jagged channel of white-hot air we call a lightning bolt get started?
Recently, the field has experienced a sort of renaissance as researchers — many of them astrophysics refugees like Dwyer — have devised new ways to pierce the clouds. They’ve taken a slew of instruments built to study violent cosmic events and trained them on the brutality of terrestrial thunderstorms. They’ve seen lightning shooting out X-rays as it zigs and zags, spotted flickering glows of gamma rays coming from thunderclouds, and, very recently, detected hints of bolts traveling in unexpected directions.
No one has put all the pieces together, but a new understanding of lightning is taking shape. The fearsome flashes look less and less like the supersize electric sparks that physicists once imagined them to be. While electricity plays a central role, lightning bolts are formed and shaped by the whole physics canon — from cosmic blasts to particle physics. In particular, triggering a bolt seems to require extreme events more typically associated with supernovas, black holes, and particle colliders than with fluffy clouds.
“There is a growing consensus in the field that high-energy processes play a critical role in lightning initiation,” said Caitano da Silva, an atmospheric physicist at New Mexico Tech. “It’s an exciting time to be in this field.”
Trigger Point
When lightning bolts split the sky, the ancient Greeks, Scandinavians, and Hindus saw flashes of divine warfare. And when thunderclaps rattled their chests, the Chinese felt a deity punishing wrongdoers. Today, the power of thunderstorms still leaves people awestruck.
“I grew up watching these large cold fronts coming in with a lot of lightning” in Brazil, da Silva said. “I grew terrified of it.”
With fear comes fascination. Yet despite centuries of exploration, fascinated physicists like da Silva are still asking the same question that the ancients did: How does lightning begin?
For a time, researchers thought they had an answer. As physicists demystified electricity in the 18th and 19th centuries, they learned how to make sizable sparks on command: pile up electric charge on one metal ball, bring a second nearby, and a spark leaps between them. When researchers eventually worked out the structure of matter, they understood why. The separated charges generate an electric field between the balls. When the electric field reaches a critical strength — roughly 3 million volts per meter — the air starts to come undone. The field flings loose electrons into neighboring atoms, where they knock more electrons loose. Like snow on a steep mountain slope, the electrons “avalanche,” heating up the air until it glows.
Mark Belan/Quanta Magazine
Benjamin Franklin linked sparks in the lab with lightning in the sky in his famous kite-flying experiment in 1752. And for the next 200 years, investigators believed that what happened in storm clouds was exactly the same as what happened between their metallic spheres, just on a larger scale. The mystery of lightning seemed solved.
But when physicists graduated from kites to rockets and truck-size weather balloons in the mid-20th century, they found a problem. Clouds do have electric fields; tiny ice crystals rub against each other like socks against a carpet, and crystals with extra electrons tend to pile up at the bottom of the clouds. But these fields are weak. Typical thunderstorms have just a tenth the electric juice needed to spark, and the strongest fields ever measured reach just a third of the critical intensity. Yet according to NASA satellites there are more than 2,000 thunderstorms across the globe at any given moment — an observation as puzzling as avalanches thundering down bunny slopes.
“You have to increase the electric field all the way above the conventional breakdown threshold,” said Michael Stock, a researcher at the Cooperative Institute for Severe and High-Impact Weather Research and Operations at the University of Oklahoma. “But that doesn’t seem to happen in nature.”
A visible bolt means the air has broken down into a mess of hot, charged subatomic debris. So either something has supercharged the electric field, pushing it past the critical threshold, or some other process must break down the air molecules. The question is: what?
Public Domain
One clue comes again from Franklin. He observed that sharp tips are more likely to start or receive a spark. Physicists now understand that this happens because pointed conductors enhance the nearby electric field. In the 1960s and 1970s, physicists in Florida and France started intentionally setting off lightning bolts by firing small rockets with sharp points into storm clouds. A wire would unspool behind the rocket and guide the bolt to the ground.
Most storm clouds don’t have rocket-mounted darts to help them spark, but they do have ice crystals, some of which can exceed the size of a pencil eraser. These ice chunks, which are also conductors, can stretch into shards. Physicists estimated that sufficiently lengthy ice shards could boost the field strength by a factor of 10 or more, and that a number of these so-called hydrometeors acting together could do even better. Once again, the mystery seemed solved.
Then physicists started looking at storms from space and learned that thunderclouds were stranger than they had imagined.
Runaway Avalanches
In 1994, a satellite searching for extreme deep-space explosions happened to pick up flashes of gamma rays coming from thunderclouds, often alongside lightning. Gamma rays are the most energetic type of light rays, typically marking the last gasp of a dying star or the cataclysmic clap of two neutron stars. They are not something you’d expect to come out of a cloud, no matter how many sharp ice chips it had. Something was afoot in the fast and intense realm of subatomic particles.
This was around the time that Dwyer witnessed the booming Floridian lightning storms and learned about their mysterious origins. As an astrophysicist, he knew about the subatomic realm. He was familiar with the work of the Nobel laureate C.T.R. Wilson, who had hypothesized that a “relativistic” electron moving at close to the speed of light would barely feel any drag from atoms in the air. (Da Silva likens it to a bullet ripping through a flurry of snowflakes.) A sufficiently speedy electron in an electric field could therefore “run away” faster and faster.
Dwyer knew that a Russian physicist, Aleksandr Gurevich, had shown in 1992 that such a runaway electron could unleash a cascade of perhaps 100,000 electrons, akin to the avalanches that initiate sparks in the lab but playing out over hundreds to thousands of meters. And he also knew that when these relativistic, runaway electrons bounced off air molecules, they could emit gamma rays.
NASA
By themselves, these extreme subatomic affairs didn’t seem to be abundant enough to account for the brilliant gamma rays lighting up storm clouds. But then Dwyer imagined a baroque process that could allow one avalanche to set off another, and another, and another, all right on top of each other.
According to Dwyer’s process, when one electron in the avalanche collided with an atom, the electron could ricochet and emit a gamma ray. That gamma ray would transform into an electron and its antimatter twin, a positron. The cloud’s electric field would push the positron backward close to where the avalanche began. There it could crash into another atom, setting off another avalanche, which would make more gamma rays, more positrons, more avalanches, and so on, until you got a flash visible from orbit.
“It’s like taking a microphone and sticking it next to a speaker,” said Dwyer, who is now at the University of New Hampshire. “It can get really loud quick.”
The stack of runaway relativistic avalanches could explain the gamma rays. And it could also contribute to lightning initiation. As the avalanche cascades, electrons pile up at the front while leaving positively charged ions in their wake — boosting the cloud’s electric field.
In computer simulations, Dwyer showed that this chain of events amplified avalanches, radiated gamma rays, and ramped up the electric field. Around the same time, detailed simulations of ice shards revealed how sharp they were likely to get — not very sharp — which also began to weaken the hydrometeor theory.
So, were Dwyer’s runaway relativistic avalanches really happening inside clouds? And could this boost the electric field enough to produce lightning? His colleagues were divided.
Researchers needed to get closer to the action. In July 2023, daredevil physicists outfitted a high-altitude NASA plane with gamma-ray detectors and flew it straight over the core of some of the most ferocious storms on the planet — tropical storms in the Gulf of Mexico, the Caribbean, and Central America. The plane reached stratospheric perches that “most people would like to avoid at all costs,” da Silva said. The campaign was called ALOFT, an acronym made in part from other acronyms. Its observations delivered the biggest bonanza of new data in a generation.
Storm clouds, ALOFT revealed, are bubbling cauldrons emitting all sorts of gamma rays that are too faint to see from space. The project confirmed the soft glows and sudden flashes around lightning that space-based instruments had also detected. But ALOFT also detected that clouds flash even when no lightning is visible. Most curiously, they also flicker.
“They discovered there’s a whole zoo of other phenomena,” said Ute Ebert, a lightning physicist at Eindhoven University of Technology in the Netherlands.
One person who wasn’t completely surprised by the ALOFT observations was Dwyer. In anticipation of the ALOFT team’s announcement, he had rerun his simulations to predict what their gamma-ray detector would see as it flew above the storms. He had long known that the relativistic avalanches unavoidably piled up in a flickering pattern, so he calculated exactly what kind of flicker the particle collisions would produce. Both teams presented their findings in San Francisco at the American Geophysical Union’s annual meeting in December 2023, and the results lined right up — the strongest evidence yet that Dwyer’s subatomic collisions are playing out inside real thunderstorms.
NASA/Carla Thomas
Now other theorists are building upon this theory. Last summer, Victor Pasko, an electrical engineer at Pennsylvania State University, studied the chain of events set off under other circumstances, such as higher electric fields, and found that in these cases too avalanches can pile up and initiate lightning, lending additional support to the whole framework.
“It’s consolidating this idea that the energetic electrons are playing a role here,” da Silva said. “Until very recently, essentially just Dwyer was talking about this.”
At Odds With The Field
Chains of high-energy electron avalanches may very likely be making clouds glow, flicker, and flash with gamma rays. But researchers can’t say with certainty that they are also sparking lightning. One puzzle is that lightning seems to start from one point in the cloud, while the avalanches take place over a much larger region. The avalanches bring the cloud close to the conditions that are expected to lead to lightning. But no one has fully connected them to the triggering of a lightning bolt.
Even as Dwyer’s theory has gained support, observations from early 2025 have revived yet another theory of lightning creation.
In the New Mexico desert, a pair of stations bristling with antennas captured radio waves coming out of a dozen separate lightning strikes. Using this data, Xuan-Min Shao, a researcher at Los Alamos National Laboratory, was able to reconstruct the way the overall current moved during the start of these strikes. He found that something was off. If one of Dwyer’s cascades, or any other process driven purely by the electric field, was seeding the lightning bolt, the proto-bolt would move perfectly in line with the electric field from the very beginning of the process. But Shao found that in these cases, the two directions were slightly at odds. In the slant, Shao sees evidence for an extraterrestrial, even extragalactic origin for lightning — a cosmic-ray shower.
Cosmic-ray showers are the end result of violent events in deep space, such as the expulsion of particles from feeding black holes or stellar explosions that fire off a piece of atomic shrapnel — perhaps a proton from an exploding star, or a denuded iron atom expelled from a supermassive black hole. These shards travel billions of light-years across the universe and slam into Earth’s atmosphere. The violent collision sprays a jet of electrons, positrons, and other particles down into a cloud at a random angle. These electrons and positrons could have enough oomph to separate the electrons from their molecules and get an avalanche going, even if the electric field stays well below the critical threshold.
To some physicists, Shao makes a strong case. “It has to be mapping the direction of something else, most likely the cosmic-ray ionization,” said David Smith, a physicist at the University of California, Santa Cruz. “I find the data extremely convincing.”
Others say it’s too soon to know what to make of the finding. Shao’s reconstruction technique isn’t fully established, and cosmic-ray showers are full of poorly understood particle physics. That makes it tempting to use them as a “magic wand,” said Brian Hare, a physicist at the Netherlands Institute for Radio Astronomy, to fill an otherwise hard-to-explain gap in a mysterious process.
But if Shao and others start to see more instances of lightning flying askew, that might motivate theorists to work out those details.
Los Alamos National Laboratory
“It’s a really cool idea, and there’s a hint that this might be going on,” Dwyer said. “If this mechanism is true, every time you see a lightning flash, there is a physical connection to a dying star somewhere in the galaxy.”
The last few decades of lightning research have produced a handful of ideas for how nature may coax lightning bolts from clouds with weak electric fields. And while the theories compete in the scientific literature, they likely collaborate in the real world. Long needles of ice may set off bolts in one cloud while a deluge of electrons producing gamma rays does it in another cloud. And multiple mechanisms may work together to push the electric field past the point of no return. Only with more precise measurements of the gamma rays and radio waves that accompany lightning can researchers hope to determine whether one mechanism, or one combination of mechanisms, is the most common.
But as physicists close in on the mystery of what initiates lightning, they’re once again spotting unexpected occurrences that don’t fit any of the theories. There are subtle patterns in the gamma rays ALOFT saw, for instance. And over the last few years, a radio telescope array in the Netherlands has been providing some of the sharpest images yet of lightning as it begins to branch out from its starting point. They show that some parts shoot out quickly, some move relatively slowly, and some sprout needles as they travel.
These features suggest that even as explanations get more comprehensive, the case of how lightning really works will keep getting reopened. “It just gets more and more bizarre the more we look,” Dwyer said. “Clearly our very simple pictures here are really incomplete.”