Lightning initiation, gamma-ray flashes and ball lightning

6 problems

• What is ball lightning?

  Open

  People have long reported glowing balls the size of a grapefruit that float for seconds after lightning strikes. No one has explained what stores the energy or made a convincing copy in the lab.

• How do collisions between ice particles charge thunderclouds?

  Open

  Thunderclouds become charged when small ice crystals bounce off soft hail pellets (graupel), each carrying away opposite charge. Why the charge goes one way or the other, and why its sign flips with temperature and cloud water content, is not understood at the molecular level.

• Is relativistic runaway a significant way thunderclouds lose charge?

  Open

  Many storms glow faintly in gamma rays for seconds to minutes. If the electron avalanches behind the glow carry enough current, they could be a hidden way that clouds discharge besides lightning.

• How does lightning start in fields far below breakdown?

  Open

  Air normally conducts only in very strong electric fields, about ten times stronger than any measured inside a storm. Something lets lightning start anyway.

• Does oxidizing silicon vapor from struck soil explain ball lightning?

  Open

  One idea is that lightning boils silicon out of soil and the floating silicon dust then slowly burns. This predicts specific light colors and lifetimes that can be checked.

• What produces terrestrial gamma-ray flashes?

  Contested

  Thunderstorms emit flashes of gamma rays lasting less than a thousandth of a second, made by electrons pushed near light speed. Whether these electrons come from the lightning tip or from a self-sustaining avalanche in the cloud field is disputed.