Water Survey researchers tracked weather changes during the eclipse

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[September 17, 2017]    CHAMPAIGN - While observers in southern Illinois looked skyward to watch August’s total solar eclipse, University of Illinois researchers studied the weather’s response, discovering significant atmospheric changes.

An Illinois State Water Survey (ISWS) team documented the eclipse at the Dixon Springs Agricultural Center in Simpson, Illinois, to learn how the atmosphere responded to rapid changes in solar radiation as the moon blocked the sun. At the same time, another team recorded climate conditions every 10 seconds at 19 Illinois locations as part of the ISWS Water and Atmospheric Resources Monitoring (WARM) program.

“Even without looking at the blocked sun or the sunset in all directions, you could tell the eclipse was occurring by changes in weather conditions,” said Jennie Atkins, manager of the WARM program. The moon covered part of the sun for three hours, as seen from the Simpson viewpoint, where the totality of the eclipse could be observed for nearly the longest time in the world (nearby Shawnee National Forest lasted slightly longer).

WARM observations showed that air temperature, which would typically rise at that time of day, actually decreased by about 5 degrees Fahrenheit, and solar radiation fell to zero during the eclipse totality. Recovery of the solar radiation took over an hour.

Also, wind speed in Simpson slowed to less than 2 miles per hour, with the minimum speed occurring shortly after the totality.

The atmosphere higher above the ground changed as well. On sunny summer days, vertical air movement, or updrafts and downdrafts, form when solar radiation heats the ground and the air slightly above it. These air movements cause areas of warm air to rise, and downdrafts to form between them. The result is often wind gusts and stronger winds at the ground, and cumulus clouds, which can form into thunderstorms.

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Shortly after the sun rose on August 21, the equipment detected weak updrafts and downdrafts reaching a short distance into the atmosphere. By the time the moon started eclipsing the sun, the updrafts and downdrafts had increased in depth, size and intensity, and towering cumulus clouds developed, according to David Kristovich, head of the Water Survey’s Climate and Atmospheric Science section.

During the 90 minutes leading up to the totality, the equipment detected rapidly weakening updrafts and downdrafts. During and shortly after totality, updrafts and downdrafts were no longer detected, and the clouds had completely disappeared.

“The changes were actually quite a bit more dramatic than I expected,” Kristovich said. “Since turbulent vertical air motions often last well into the evening, I was expecting some residual updrafts and downdrafts to last throughout the event. I was surprised that the changes in the atmosphere would be that fast.”

Ongoing research should reveal the story that the monitoring sites and equipment data are telling us, Kristovich said.

[Lisa A. Sheppard]

The Illinois State Water Survey is one of five state surveys that make up the University of Illinois’ Prairie Research Institute (PRI). PRI provides objective expertise, data, and applied research to aid decision making and provide solutions for government, industry, and the people of Illinois.



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