HUNTSVILLE, Ala. - A team of scientists and students from The University of Alabama in Huntsville (UAH) will join scientists from around the world and millions of tourists streaming into the path of a total solar eclipse that will span the U.S. from coast to coast on August 21.
Unlike most of the scientists setting up between Oregon and South Carolina, however, Kevin Knupp and his team from UAH won't be watching the eclipse - at least not with scientific instruments. Instead, they will watch the rest of the sky... with an occasional glance at the eclipse.
Instead of measuring the sun's corona, the team from UAH's Severe Weather Institute, Radar and Lightning Laboratories wants to watch clouds dissipate as the sun's heat disappears. They want to measure how quickly columns of warm air rising into the hot summer sky wither away as cooler air starts to puddle at or near the surface, when they aren't using their instruments to count bugs.
"We've been looking at the afternoon-to-evening transition for years," said Knupp, a professor of atmospheric science at UAH. "What an opportunity for us to study in fast motion something we've been studying at regular speed for the past eight years."
While the period of total darkness during the eclipse will last less than three minutes (a maximum of about 2 minutes and 40 seconds at Hopkinsville, KY), the period of 50 percent solar coverage could be upwards of an hour, "which is long enough to disrupt the daytime boundary layer at a time that would see maximum solar heating except for the eclipse," Knupp said.
The daytime boundary layer is filled with columns of convective updrafts that rise into the atmosphere as Earth's surface is warmed by the sun. In the southeastern U.S., summer convection sends those warm currents of air rising as much as 5,000 feet above the surface.
Those updrafts contribute to the formation of cumulus clouds - the puffy white clouds that float about on warm summer days and which are known to quickly dissipate.
"You can document thermal activity by watching cumulus clouds," Knupp said. "We will have cameras taking time-lapse pictures of the clouds that day so we can study how the clouds respond to the eclipse. The transformation in cloud behavior will be compared to changes in boundary layer updrafts measured by three mobile profiler systems and one mobile Doppler radar. The hypothesis is that cumulus clouds connected to thermals should dissipate.
"At the same time, cloud fields in active convergence zones — such as you might see where warm and cold air masses collide or in places where you have land and sea breezes — those organized cloud fields could intensify. It's well known that convective storm formation can be quite active at dusk."
The UAH team will position the profilers — which map the vertical structure of the atmosphere — and the Doppler radar at four locations from Clarksville, TN, and Hopkinsville, KY, to Land Between the Lakes in western Kentucky. The UAH team will set up the day before the Aug. 21 eclipse so they can go out that morning to collect data on the local night-to-day transition.
They also will stay in place after the eclipse, so they can gather data at dusk to compare against the dusk caused by the eclipse earlier that day.
In addition to the radars, lasers and other electronic instruments, Knupp's team will launch weather balloons into the stratosphere. A balloon tethered at 100 meters high will provide high-resolution data about temperatures just above the Earth's surface.
The goal, he said, is to collect the most comprehensive dataset on eclipse-induced changes to the boundary layer to date.
Working with colleagues from Tennessee's Austin Peay University, the UAH team also wants to use its advanced Doppler radar to see if daytime-flying insects land and nighttime-flying insects take off during the brief "night," which might offer clues to whether their flight schedules are controlled by the turning of the days or by tiny internal clocks.
The general radar and profiler "signatures" that distinguish between daytime bugs and nighttime bugs are complicated in the Southeast by the presence of bats, which also emerge about at sunset. In the case of a midday eclipse, the bats shouldn't be present if their habits are controlled by their internal clocks.
"Daytime insects tend to be more passive in their flights," Knupp said. "They tend to float with the thermals in the convective boundary layer. The air is full of bugs, especially on clear days when convection is strong."
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As the sun moves low in the sky, however, "there's a lull," he said. "After sunset there's a rapid expansion. In tens of minutes a rapid transition occurs from very little insect return to heavy coverage, which we can detect out beyond 100 kilometers.
"That's the insect bloom that occurs on a pretty regular basis during the warm months. About sunset, out they come."
Night-flying insects can fly high, Knupp said. "Using profilers, we've detected insects up to four kilometers above the ground. That's getting up toward the freezing level."
Although Knupp's team of 16, including seven graduate students and seven undergrads, will focus on collecting weather data, they will take time to observe the eclipse, he said. "We've gotta do that."
He also is aware of forecasts of huge crowds and potentially transcontinental traffic gridlock along the path of the eclipse. He is worried about getting from his room in Clarksville to the vertical profiler in Hopkinsville on Monday morning.
"I don't know how easy it will be to get around," he acknowledged. "I'm even tempted to camp out at Hopkinsville and sleep in the van. Honestly, I don't know what to expect, so I'm expecting the worst."