By — . The moment the sun went behind the moon, the snapping turtles all simultaneously slipped into the waters of Lake Tawakoni. Twilight painted the world. Clouds raced across the sky. Just beside the moon-covered sun sat bright Jupiter, shining in the middle of the day. Most birds and insects had grown hushed or gone completely silent. It’s hard to fully encapsulate the feeling of a total solar eclipse; how it changes in your surroundings, how the temperature drops so suddenly that you unexpectedly shiver ( ). But on April 8, I and millions of people across North America got to witness a celestial wonder. I’d ventured to Wills Point, about an hour east of Dallas, to meet up with Darci Snowden, a space physicist at Central
Washington University in Ellensburg and her undergraduate students. From a wooden pier, they were sending up weather balloons to capture data, delighting local families who gathered to watch the balloons ascend into the sky. For days leading up to the eclipse, the forecast in
Texas had been poor, with potential thunderstorms and cloud cover blocking the skies. When things finally shook out, we had a nice long period of cloudless sky as the
moon moved in front of the sun, turning it into a sliver. Just at the moment of totality, a big cloud came by, leading to groans all around. Luckily, the sun’s usually invisible atmosphere, the corona, broke through patches in the clouds. Tiny red dots could be seen at the sun’s edges — fiery flares erupting from its surface. Cloudy or clear, there was still science to be done. Total solar eclipses provide rare opportunities to study the sun and its impact on Earth in unprecedented ways. Here in Wills Point, starting at 2 p.m. CDT the day before the April 8 eclipse, Snowden’s team began launching a series of 30 weather balloons. The plan was to loft one every hour, all through the night, continuing for six hours after the eclipse. Buoyed by helium, these balloons are capable of soaring to a height of 33 kilometers (20 miles) into the stratosphere, the atmosphere’s second-lowest layer. They carried battery-powered instrument packages called radiosondes to collect such data as temperature, humidity, pressure, and wind direction and speed. Snowden and her students hope to get detailed information on how an out-of-the-ordinary event like a total solar eclipse affects Earth’s atmosphere. They are studying what happens in the atmosphere’s lowest region, known as the planetary boundary layer, which reaches a height of around two kilometers and blankets Earth’s surface. Changes in this layer are driven by two things: the topology of the ground, including objects such as mountains, buildings and forests; and solar radiation raining down from above. In particular, the team is looking for evidence of gravity waves. Not to be confused with gravitational waves — ripples in the fabric of spacetime occurring when massive astronomical objects like black holes collide — gravity waves are a more down-to-earth phenomenon. They can occur when pockets of air are forced upward by something like a mountain range and then are pulled back down by the force of gravity, creating a periodic oscillation that can carry energy through the atmosphere. Rapid temperature changes can also set them off. As cool air becomes denser and sinks, it sometimes sinks so low that it overshoots its equilibrium point and then floats back up, generating a wave. “It’s a little like pushing down an ice cube in a glass of water,” Snowden says. During the last U.S. total solar eclipse in 2017, a team of scientists flew balloons outside the path of totality in Wyoming and
New York and found hints that the shadow of the moon racing across the atmosphere close to the ground that moved outward like bow waves from a traveling ship. Such a phenomenon had been predicted nearly 50 years prior but never definitively seen. During that same 2017 event, eclipse-driven gravity waves were conclusively spotted for the first time ( ). This time around, Snowden is hoping to confirm the previous hints of their existence in lower atmospheric layers. The goal of the balloons launched 24 hours prior to totality, when the moon completely blocks the sun, was to collect baseline readings before the eclipse. These could then be compared to the measurements taken during and after the event. Such data could help lead to better short-term weather and long-term climate predictions. While gravity waves are among the smallest atmospheric waves that scientists study, their effects can be significant. They influence turbulence, transfer heat and mix airborne chemicals all over our planet. Many travel vast distances, sometimes
BREAKING like ocean waves 500 or more kilometers above Earth’s surface. Getting the team’s weather balloons up just before and after totality was “definitely stressful,” says Eli Pugsley, a senior physics major who was helping to lead the launches. “But once we got into a rhythm, everybody does their
Job and it goes really smoothly.” The students’ data will be compiled alongside that from around 40 other teams with NASA’s , who were also launching weather balloons along the path of totality. Taken together, the information may determine if the eclipse produced gravity waves in the lower atmosphere, though processing and analyzing the data will take about a year, Snowden says. Other eclipse-related experiments were being conducted all over the country by and groups of alike, while crowds of eclipse watchers poured into towns all along the path of totality hoping for a cloud-free view of the celestial phenomenon ( ). At the University of Texas, Dallas campus, for instance, physicist Fabiano Rodrigues and his team had their eyes on the ionosphere, which starts around 80 to 90 kilometers above the surface. Solar radiation bombards the thin atmospheric gases in this layer, ripping apart their atoms into electrons and nuclei, a process called ionization. At night, free from the solar barrage, these ions have a chance to recombine. Similar changes happen during the sudden shift to darkness during a total solar eclipse. Rodrigues and his students placed cheap, off-the-shelf devices capable of receiving satellite signals, such as GPS, in a giant triangle: one on campus, one around 100 kilometers to the north, and the third about 50 kilometers east in the town of Terrell. These detectors watch the of electron content in the ionosphere, a proxy for how ionized it is. The data Rodrigues and his team collected during the eclipse could help confirm predictions of just how much the ionosphere will deionize in response to the loss of sunlight from the eclipse, or where these predictions are still coming up short. Such data will be used to learn how changes in the ionosphere affect and degrade the satellite transmissions that are so crucial for such things as communication and navigation, so that engineers can compensate for those impacts in the future. Electron counts in the ionosphere dipped just as expected during the event, Rodrigues says, though it will likely take at least a few days before he can figure out which models made the most accurate predictions. Despite some cloud cover in Dallas, he’s quite pleased with how things shook out. Meanwhile, as the sun brightened back to its normal levels above Lake Tawakoni, Snowden and her team were able to take a moment to reflect on what they’d just witnessed before returning to their balloon launches. “It’s an amazing experience,” she says. “And I feel really fortunate to have seen it.” J. Fowler . . , Vol. 100, June 2019. doi.org/10.1175/BAMS-D-17-0331.1. B.J. Harding . . , Vol. 45, April 28, 2018, p. 3366. doi: . Adam Mann is ’ temporary astronomy writer. He has a degree in astrophysics from University of
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