科学美国人60秒:Sun's Magnetic Field Boosts Earth Lightning

You might think of weather as a local—or regional—phenomenon. But when it comes to lightning storms, what happens 93 million miles away… at, you guessed it, the Sun… can actually affect the frequency of thunderbolts. That's according to a study in the journal Environmental Research Letters. [M J Owens et al: Modulation of U.K. lightning by heliospheric magnetic field polarity]

"So the Sun is essentially a bar magnet. And as it rotates around half the time its field points towards the Earth and half the time its field points away from the Earth." study author Mathew Owens, an environmental physicist at the University of Reading in the U.K. He and his colleagues analyzed lightning strikes in the U.K. over a six-year period. And they found that when the Sun's magnetic field was pointed away from the Earth, lightning strikes in the U.K went up 50 percent. Owens says what they think is happening is the Sun's magnetic field affects the Earth’s magnetic field, stretching and skewing it, which allows more cosmic rays to hit the atmosphere. 

That's important, because cosmic rays can trigger lightning. "Some groups in America do outrageously cool things like fire rockets with metal wires attached to them into clouds. And that directly triggers the lightning. Because the lightning has a nice metal wire to travel down." 

Nature doesn't do that, of course. But cosmic rays serve a similar purpose. "These energetic particles that are coming from space essentially produce thin channels of ionization that behave like a thin metal wire. And that enables lightning to occur from the bottom of the cloud to the Earth."

These types of studies could eventually improve lightning forecasts, Owens says. And since lightning strikes are predicted to increase in a warming world…we may end up seeing less of the Sun itself… but more of its electrifying influence.

—Christopher Intagliata