Air pollution, which gives as trouble with breathing clean air, is also found to cause larger and longer-lasting storm clouds. Researchers linked in to aerosols.
Atmospheric Scientist Jiwen Fan, together with her co-researchers from the Department of Energy’s Pacific Northwest National Laboratory, have discovered that instead of the initial belief that pollution causes larger and longer-lasting storm clouds by making thunderheads draftier through a process known as convection, it makes clouds hang around by lessening the size and augmenting the lifespan of cloud and ice particles.
“This study reconciles what we see in real life to what computer models show us. Observations consistently show taller and bigger anvil-shaped clouds in storm systems with pollution, but the models don't always show stronger convection. Now we know why,” Fan told Phys.org.
Additionally, through those clouds, pollution can lessen the daily temperature range. High clouds left after a thunderstorm sprawl across the sky and look like anvils. These clouds chill the Earth with their shadows at daytime, but at night time, acts like a covering that entrap heat.
Though researchers have concluded so, they are still wondering why these clouds stay longer in polluted skies than clean skies. They linked it to tiny natural and manmade particles called aerosols. Aerosols act as seeds for cloud droplets to form around.
Polluted skies have more aerosols, which may mean less water for each seeds. They also make more, tinier droplets, which can start a chain reaction that may lead to larger and longer-lasting clouds. Through stronger convection, these tinier droplets will bring their water higher where they will eventually freeze. The freezing of water droplets squeeze out the heat carried by the droplets, thus causing a draftier thunder cloud.
However, researchers don’t always see stronger convection every time they see larger and longer-lasting storm clouds in polluted air.
To find the missing piece of the puzzle, Fan and her co-researchers decided to compare a real-life summer storm cloud and a computer cloud model that zooms deep into virtual clouds that include physical properties. The experimentation lasted for six months.
They also studied clouds from three different locations -- the tropics in the western Pacific, southeastern China and the Great Plains in Oklahoma. The simulations came up with a similar outcome as the virtual cloud models.
The researchers concluded that in all cases, except for two, pollution increased storm cloud sizes, thickness and period of anvil-shaped clouds. This suggests that larger and longer-lasting storm clouds are not due to stronger convection.
Upon deeper analysis, the researchers found out that ice crystals in polluted skies are smaller compared to the ice crystals formed in the clear skies. Since ice crystal formed in polluted skies are smaller, they were also too light to fall out of the clouds, thus contributing to larger and longer-lasting clouds.
This study was published in the Proceedings of the National Academy of Sciences.
