Land Vs. Sea

The oceans provide the “fuel” for almost all the thunderstorms on Earth: water that evaporates from the ocean surface. But the oceans generally don’t provide the “trigger” for the big storms. As one indication of the difference, about 90 percent of all lightning happens over land.

A thunderstorm forms when warm, humid air rises high into the atmosphere and condenses to make clouds. The humidity comes from the oceans. Storms in the Great Plains, for example, are fed by water vapor from the Gulf of Mexico. And the summer monsoon in the Southwest is fed by the Gulf of California.

But the storms need a strong source of heat to get the water vapor to rise high enough to form clouds. During the warm portion of the year, the land gets hotter than the oceans. There’s also a bigger contrast on land—some areas heat up more quickly, so they’re more likely to start building the clouds. Terrain also plays an important role—mountains can push air upward. In contrast, the oceans are more stable, so there’s not much to trigger big storms.

Oceans do outperform the land in one way, though—they produce more “superbolts” of lightning. Such bolts can be a thousand times more powerful than a typical discharge. That appears to be because the salt content makes ocean water a better conductor of electricity than soil or fresh water. So when a thunderstorm does form over the ocean, it’s much more likely to produce a really spectacular light show.

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