The scientists conducted a computational study with resolutions high enough to allow the team to see the clouds develop. They found that for warm summer thunderstorms, pollution particles lead to stronger storms with larger, anvil-shaped clouds that also last longer. The warming effect dominated by trapping more heat, especially at night, even though the larger clouds also reflected more sunlight warmth back into space during the daytime.

Previous work showed that when it's not too windy, pollution leads to bigger clouds. This occurs because more pollution particles divide up the available water for droplets, leading to a higher number of smaller droplets that are too small to rain. Instead of raining, the small droplets ride the updrafts higher, where they freeze and absorb more water vapor. Collectively, these events lead to bigger, more vigorous convective clouds that live longer. DOE researchers from PNNL, and scientists from Hebrew University in Jerusalem and the University of Maryland took to high-performance computing to study the invigoration effect on a regional scale. The simulations had a high enough resolution to allow the team to see the clouds develop. The researchers then varied conditions such as wind speed and air pollution. This is the first time researchers showed pollution increased warming by enlarging thunderstorm clouds. The warming was surprisingly strong at the top of the atmosphere during the day, when the storms occurred. The pollution-enhanced anvils also trapped more heat at night, leading to warmer nights.