Storm force

Scientists have known for decades that thunderstorms are often stronger where there are high concentrations of aerosols-airborne particles too small to see with the naked eye. Lightning flashes are more frequent along shipping routes, where freighters emit particulates into the air, than in the surrounding ocean. And the most intense thunderstorms in the tropics brew up over land, where aerosol levels are elevated by both natural and human-caused phenomena.

Now MIT scientists using idealized simulations of cloud dynamics have found that low-lying clouds with high aerosol concentrations are less likely to release water as rain. Instead, their water evaporates, creating a humid layer that makes it easier for air to rise quickly through the atmosphere as strong, storm-brewing updrafts.

After you've established this humid layer relatively low in the atmosphere, you have a bubble of warm and moist air that can act as a seed for a thunderstorm," says grad student Tristan Abbott, who coauthored a paper on the research with assistant professor of atmospheric science Tim Cronin. They say this humidity-entrainment" mechanism, as they call it, could be incorporated into weather and climate models to help predict how a region's thunderstorm activity might vary with changing aerosol levels.

It's possible that by cleaning up pollution, places might experience fewer storms," says Cronin.