Texas Researchers Find Cloud-Feeding Aerosols May Be To Blame For Extreme Weather

AUSTIN, TX -- Come winter, you might want to hold off on firing up the wood-burning fireplace. If not, you'll need to deal with the guilt of contributing to the more extreme storms we've been experiencing by increasing clouds' life spans.

You might be asking: How is this even possible, and what is the connection?

According to new research by the University of Texas at Austin, an abundance of aerosol particles in the atmosphere can increase the life span of large storms clouds by delaying rainfall -- making said clouds enlarge and live longer, producing even stronger storms than they had otherwise planned on unleashing.

The study was published in the journal Proceedings of the National Academy of Sciences on June 13, and is the first to address the impact that aerosol particles have on the lifespans of large thunderstorm systems called mesoscale convective systems, university officials said.

"These storms are complex, often violent systems that can span over several hundred kilometers," officials said. The systems are “...the primary source of precipitation over the tropics and mid‐latitudes, and their lifetime can have a large influence on the variability of rainfall, especially extreme rainfall that causes flooding,” noted the paper.

The research was led by scientists from The University of Texas at Austin Jackson School of Geosciences. The work was based on analysis of data from 2,430 convective cloud systems, finding that aerosols can help increase the lifespans of convective cloud systems by as much as three to 24 hours, depending on regional meteorological conditions, university officials explained.

“A cloud particle is basically water and aerosols. It’s like a cell. The aerosol is the nucleus and the water is the cytoplasm,” said lead author Sudip Chakraborty, who recently received his Ph.D. from the Jackson School. “The more aerosols you have, the more cells you get. And if you have more water, you should get more rain.”
Researchers from the University of Colorado Boulder and NASA’s Jet Propulsion Laboratory also worked on the study.

Before reading on, a primer on aerosols: They are tiny particles in the atmosphere that form the nucleus within a cloud around which water condenses to form the cloud. They can originate naturally from such sources as volcanic eruptions or desert dust, or human-made sources such as the burning of wood, coal or oil.

University officials claim the study represents the first attempt to try to look at aerosols’ relative importance in the lives of storm clouds compared with meteorological conditions such as relative humidity, available convective energy and wind shear, said Rong Fu, a professor in the Jackson School Department of Geological Sciences and co-author of the study. Although meteorological conditions remain the most important element in the lifetime of a convective cloud system, Fu said the research shows that aerosols have a significant impact.

This isn't the first time the aerosol-cloud connection has been identified. NASA in 1996 examined the interplay as well.

"Aerosols interact both directly and indirectly with the Earth's radiation budget and climate," NASA researcherssaid. "As a direct effect, the aerosols scatter sunlight directly back into space. As an indirect effect, aerosols in the lower atmosphere can modify the size of cloud particles, changing how the clouds reflect and absorb sunlight, thereby affecting the Earth's energy budget."

But the UT paper is the first to blame aerosols on the type of extreme weather that appears to be growing in prevalence. In that respect, it's close to an indictment of those pesky, minute particles as you're likely to see from the staid, buttoned-down halls of academia.

It wasn't easy to level this charge. One of the challenges is that satellites providing data on cloud aerosol content typically pass over the same part of the Earth twice a day -- yielding insufficient data on the lifetime of a convective cloud system, Fu said. But Chakraborty was able to break new ground by using data from geostationary satellites that fly much higher and stay in the same location relative to the Earth’s surface, researchers said.

“He painstakingly matched the geostationary satellite data, which gives you some information about the lifecycle of the convective systems, with data from the polar orbital satellite that passes by twice a day,” Fu said. “He really raised the bar for how we analyze satellite data.”
One of the world's preeminent researchers in the field, professor Daniel Rosenfeld of the Hebrew University of Jerusalem, added that aerosols’ effects on deep convective clouds and climate have been major, looming questions confounding researchers for more than a decade.

Of particular interest, Rosenfeld said, is the role of clouds in reflecting solar radiation and emitting thermal radiation to space, which can influence the radiative balance in the atmosphere and the Earth’s temperature. This study, the professor added, significantly advances the science.
“This is the first study that shows the full life cycle of convective clouds in a statistically meaningful way on a climate scale,” said Rosenfeld, who did not work on the paper. “This is an important step towards determining the impact of clouds on radiative forcing. The next step is to quantify.”

You may never look at clouds quite the same way again.