The mystery of the initial spark may have been solved

Nature · Published 26 October 2026 Swipe more like this →

In short: For decades, scientists couldn't explain how a cloud suddenly generates enough power to create lightning. While we knew about charge separation, the actual trigger remained elusive. New observations of rare, powerful discharges suggest that the primary mechanism for these massive electrical bursts is moving in a direction no one expected.

Lightning occurs when positive and negative charges separate within a cloud—a process driven by collisions between heavy graupel particles falling downward and lighter ice crystals carried upward by turbulent updrafts. This separation creates the potential for electricity to flow, but scientists have long struggled to identify what actually initiates that first spark. Since the 1990s, a dominant hypothesis proposed that 'negative breakdown'—where sparks travel from negative to positive areas—originated via relativistic runaway electron avalanche or high-energy cosmic rays.

However, researchers at the New Mexico Institute of Mining and Technology have identified a rare but extremely powerful discharge known as narrow bipolar events. Using a broadband interferometer to observe these events, they discovered that the spark actually moves downward from a positive region to a negative one. This is known as 'fast positive breakdown.' The data suggests this specific type of downward-moving discharge may initiate most, if not all, of the lightning flashes typically observed in thunderstorms.

This discovery challenges previous computer simulations and laboratory theories because it contradicts the expected behavior of relativistic electron avalanches. Moving at 10 million to 100 million meters per second, these compact bipolar occurrences generate radiofrequency radiation reaching several megawatts, representing the planet's most potent natural RF sources. By identifying positive breakdown as the primary trigger, scientists can better understand how clouds generate currents powerful enough to overcome the atmospheric barriers that currently appear too weak to initiate lightning.

This shift in understanding matters because it provides a clearer mechanism for how nature manages massive energy transfers. While laboratory environments cannot replicate the kilometer-scale conditions of a thunderstorm, these observations offer a new roadmap for modeling one of Earth's most powerful and mysterious natural phenomena.

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