Aerosols in the atmosphere may cause tropical thunderstorms to be more severe

Researchers at MIT have been conducting observations of Earth's atmosphere, looking at aerosols created by natural sources and human activities. According to the results of their observations, thunderstorms are often stronger in the presence of high concentrations of aerosols, which are airborne particles too small to see with the naked eye. The team found that lightning flashes are more frequent along shipping routes where freighters often more emit particles into the air compared to the surrounding ocean.

More intense thunderstorms were also found in the tropics over land where aerosols are elevated by natural sources like forest fires and human-made pollution. The link between aerosols and thunderstorms had been observed for decades, but what caused that link was a mystery. That mystery has now been solved.

MIT researchers used idealized simulations of cloud dynamics and found that high concentrations of aerosols enhance thunderstorm activity by increasing humidity in the air surrounding the clouds. The mechanism that occurs between aerosols and clouds is called the "humidity-entrainment" mechanism and may be incorporated into weather and climate models to predict how thunderstorm activity in a region might vary with changing aerosol levels.

Researcher Tim Cronin, assistant professor of atmospheric science at MIT, says that by cleaning up pollution areas might experience fewer storms. Researchers consider an aerosol any collection of fine particles suspended in the air. Aerosols can be created by anthropogenic processes like burning biomass, combustion, factories, car exhaust, volcanic corruptions, sea spray, and dust storms.

Aerosols act as seeds for cloud formation in the atmosphere, and suspended particles serve as an airborne surface allowing water particles to condense to form individual droplets that hang together as a cloud. Those droplets collide merged to form bigger droplets that eventually fall as rain. When aerosols are highly concentrated, many tiny particles from equally tiny cloud droplets, which don't easily merge.

The researchers devised a theory that if the surrounding air was dry, it could soak up more of the cloud's moisture and bring down the internal temperature causing the clown to rise slower through the atmosphere. If the air is relatively humid, the cloud would be warmer as it evaporates, rising more quickly and generating an updraft that could create a thunderstorm. In a cloud with many aerosol particles that suppress rain, it might evaporate more water to the surroundings increasing the humidity of the surrounding air leading to a better environment for the formation of thunderstorms.