WILLS POINT, Texas — Pitter-patter. The instant the sun disappeared behind the moon, the snapping turtles all synchronously slipped into the waters of Lake Tawakoni. Dusk adorned the world. Clouds hurried across the sky. Just adjacent to the moon-veiled sun gleamed luminous Jupiter, radiating in the midst of daylight. Most birds and insects had grown quiet or vanished completely.
Describing the sensation of a total solar eclipse fully is challenging; how it alters the character of the light in your environment, how the temperature plummets so abruptly that you unexpectedly shiver. But on April 8, I and countless individuals across North America had the privilege to witness a celestial marvel.
I had journeyed to Wills Point, approximately sixty minutes east of Dallas, to rendezvous with Darci Snowden, a space physicist from Central Washington University in Ellensburg, along with her undergraduate pupils. Positioned on a wooden dock, they were launching weather balloons to gather data, enchanting local families who congregated to witness the balloons ascend into the heavens.
In the days leading up to the eclipse, the weather forecast in Texas had been unfavorable, with potential thunderstorms and cloud cover obscuring the skies. When everything finally settled, we enjoyed a prolonged period of clear sky as the moon advanced in front of the sun, transforming it into a slender crescent. Precisely at the moment of totality, a large cloud drifted over, eliciting groans from all present. Fortunately, the sun's typically unseen atmosphere, the corona, penetrated through breaks in the clouds. Minute red dots were visible at the sun's periphery — fiery eruptions emanating from its surface.
Regardless of cloud cover, scientific endeavors persisted. Total solar eclipses offer exceptional opportunities to investigate the sun and its effects on Earth in unparalleled ways.
Here in Wills Point, commencing at 2 p.m. CDT on the day preceding the April 8 eclipse, Snowden's team initiated a sequence of thirty weather balloon launches. The objective was to release one balloon every hour, throughout the night, and continue for six hours after the eclipse. Lifted by helium, these balloons have the capability to ascend to an altitude of 33 kilometers (20 miles) into the stratosphere, the second-lowest layer of the atmosphere. They carried instrument packages powered by batteries, known as radiosondes, to collect data such as temperature, humidity, pressure, and wind direction and velocity.
Snowden and her students aspire to gather detailed insights into how an extraordinary occurrence like a total solar eclipse impacts Earth's atmosphere. They are examining the dynamics within the atmosphere's lowermost layer, referred to as the planetary boundary layer, which extends to a height of approximately two kilometers and envelops Earth's surface. Changes in this stratum are influenced by two primary factors: the terrain features, encompassing elements such as mountains, structures, and woodlands; and solar radiation emanating from above.
Specifically, the team is seeking indications of gravity waves. These should not be mistaken for gravitational waves — disturbances in the spacetime continuum occurring when massive celestial entities such as black holes collide. Gravity waves represent a more terrestrial phenomenon. They can manifest when air masses are forcefully propelled upward, for instance, by a mountain range, and subsequently pulled downward by gravitational force, resulting in a cyclical oscillation capable of transmitting energy throughout the atmosphere. Sudden fluctuations in temperature can also trigger their occurrence. As colder air becomes denser and descends, there are instances when it sinks beyond its equilibrium point and then rebounds upward, generating a wave.
"It's akin to pressing down on an ice cube in a glass of water," remarks Snowden.
During the previous total solar eclipse in the United States in 2017, a group of researchers released balloons outside the totality path in Wyoming and New York. They discovered indications suggesting that the moon's shadow moving across the atmosphere generated gravity waves near the ground, which propagated outward akin to bow waves trailing a vessel in motion. Such a phenomenon had been predicted nearly five decades earlier but had never been definitively observed. Additionally, during the same 2017 event, gravity waves triggered by the eclipse were conclusively identified for the first time at higher atmospheric levels.
In the present instance, Snowden aims to validate the previous indications of gravity waves' existence in the lower layers of the atmosphere. The objective of launching balloons 24 hours before totality, when the sun is completely obscured by the moon, was to gather baseline data ahead of the eclipse. These readings could then be compared with measurements obtained during and after the eclipse.
This data could potentially contribute to enhanced short-term weather forecasts and long-term climate predictions. Although gravity waves are among the smallest atmospheric disturbances studied by scientists, their impacts can be substantial. They influence turbulence, heat transfer, and the dispersal of airborne substances across the globe. Many of these waves traverse vast distances, occasionally breaking similar to ocean waves at altitudes of 500 kilometers or more above Earth's surface.
Eli Pugsley, a senior physics major assisting with the launches, described the process of getting the team's weather balloons airborne just before and after totality as "undoubtedly stressful." However, he added that once they established a rhythm, everyone executed their tasks efficiently, resulting in smooth operations.
The students' findings will be amalgamated with data collected by approximately 40 other teams participating in NASA's Nationwide Eclipse Ballooning Project, who were also launching weather balloons along the totality path. When combined, this wealth of information could ascertain whether the eclipse generated gravity waves in the lower atmosphere. However, Snowden notes that processing and analyzing the data will require approximately a year.
Across the country, various eclipse-related experiments were being conducted by both researchers and groups of citizen scientists alike. Meanwhile, throngs of eclipse enthusiasts flocked to towns situated along the totality path, hoping for an unobstructed view of the celestial phenomenon.
At the University of Texas, Dallas campus, physicist Fabiano Rodrigues and his research group focused their attention on the ionosphere, commencing around 80 to 90 kilometers above the Earth's surface.
Solar radiation relentlessly bombards the sparse atmospheric gases in this stratum, fragmenting their atoms into electrons and nuclei through a process known as ionization. During the absence of solar illumination at night, these ions have the opportunity to recombine. A similar phenomenon occurs during the abrupt transition to darkness experienced during a total solar eclipse.
Rodrigues and his students strategically positioned cost-effective, readily available devices capable of receiving satellite signals, such as GPS, in a large triangular formation: one on the university campus, another approximately 100 kilometers to the north, and the third roughly 50 kilometers east in the town of Terrell. These sensors monitor the real-time fluctuations in electron content within the ionosphere, serving as an indicator of its ionization levels.
The data collected by Rodrigues and his team during the eclipse holds the potential to validate forecasts regarding the extent to which the ionosphere will deionize in response to the diminished sunlight during the eclipse, or identify any discrepancies in these predictions. Such data will be instrumental in understanding how alterations in the ionosphere impact and disrupt satellite transmissions, crucial for tasks such as communication and navigation. Consequently, engineers can develop strategies to mitigate these impacts in future endeavors.
According to Rodrigues, electron counts in the ionosphere decreased precisely as anticipated during the event, although it may require several days to determine which models provided the most accurate forecasts. Despite encountering some cloud cover in Dallas, he expresses satisfaction with the outcome.
While the sun resumed its customary brightness above Lake Tawakoni, Snowden and her team seized a brief opportunity to contemplate the spectacle they had just witnessed before resuming their balloon launches.
"It's an extraordinary encounter," she remarks. "And I consider myself incredibly fortunate to have had the chance to witness it."
