CLEMSON, South Carolina - Clemson University physicists will conduct a pair of three-year rocket missions funded by NASA Heliophysics designed to deepen our understanding of the visible and invisible mechanisms that modulate energy into Earth's atmosphere.
Stephen Kaeppler is the principal investigator on a project titled "INCAA," which will study how energy is transferred and dissipated during colorful active auroras. Kaeppler has been awarded a $1.7 million collaborative grant. INCAA stands for "Ion-Neutral Coupling during Active Aurora."
Gerald Lehmacher is the principal investigator on a project titled "VortEx," which will study how turbulence and other dynamic activities that occur far above the Earth's surface affect our planet's atmosphere. Lehmacher has been awarded a $967,000 collaborative grant. VortEx stands for "Vorticity Experiment."
Clemson University's department of physics and astronomy has had a long history of involvement using sounding rocket experiments to investigate the Earth's upper atmosphere. These latest missions will continue to provide opportunities for undergraduate and graduate students who want to become involved in all aspects of a NASA rocket mission from design to data analysis. The latest projects will begin this year and conclude in 2022. The launches are planned for 2021 and 2022. The countdown has begun.
The wonder of auroras
Auroras are splendorous light shows that appear in the sky in many vivid colors, including green (the most common), red, yellow, blue and violet. Auroras occur when charged particles cast from the distant sun collide with oxygen, nitrogen and other gaseous particles in the Earth's atmosphere. When auroras occur in the Northern Hemisphere, they are called Aurora Borealis or Northern Lights. In the Southern Hemisphere, they are called Aurora Australis or Southern Lights. Both occur relatively close to the Earth's poles, where our planet's magnetic shield - which deflects most of the sun's charged particles - is weakest.
Kaeppler's project will delve into the movement and dissipation of energy during active auroral events. His team will develop state-of-the-art instrumentation that will be launched in two sounding rockets from the interior of Alaska at Poker Flat Research Range, the largest land-based rocket research range in the world. After reaching a height of about 100 kilometers, the instrumentation will activate.
"One of the things my group will look at, in particular, is how the flow of energy from distant space enters the atmosphere and where it goes from there," said Kaeppler, an assistant professor in the College of Science's department of physics and astronomy. "We're going to measure at what altitudes the energy dissipates. The light of the auroras is a visual indicator of this flow of energy. But our research will probe deeper into how the Earth's atmosphere regulates this energy transfer and also what effects this energy input has on the atmosphere."
The sounding rockets that will be used by Kaeppler and Lehmacher will be 60 to 70 feet tall and weigh several thousand pounds. They are composed of a solid-fuel rocket motor and a science payload. When the rocket motor expends its fuel, it separates from the payload and falls away. The payload continues to rise for a period of time as it conducts its experiments.
In Kaeppler's project, a suite of plasma and neutral experiments will measure electric and magnetic fields, neutral winds, background atmospheric density and the drift of electrically charged atoms. The team will also use ground-based instruments and analyze the resulting data and compare it with model-runs provided by Xian Lu, an assistant professor of physics and astronomy at Clemson.
Members of Kaeppler's atmospheric team at Clemson include Miguel Larsen, Lehmacher and Lu. Other institutions in the collaboration include the University of California-Berkeley, University of Calgary and University of Alaska-Fairbanks.
"Myself and others here at Clemson have been studying auroras for years," Kaeppler concluded. "And the more I've studied them, the more fascinated I become. They are so beautiful, so extraordinary."
Turbulence in the mesosphere
The Earth's atmosphere is a five-layered mass of air surrounding the planet. The first layer is the troposphere, which starts on the surface of the planet and extends upward to between 8 and 14 kilometers (5-9 miles). Next is the stratosphere, which is about 35 kilometers thick (22 miles). Third is the mesosphere, which is also about 35 kilometers thick. Fourth is the thermosphere, which is about 513 kilometers thick (319 miles). And finally, there is the exosphere, which is about 1,000 kilometers thick (620 miles). There is also the ionosphere, which overlaps the thermosphere and parts of the mesosphere and exosphere but is not considered a distinct layer.
Turbulent processes are found everywhere in Earth's atmosphere, but none more so than in the mesosphere, where winds often surpass 400 mph, dwarfing the speeds produced by Category 5 hurricanes. This intense conflagration of crashing, swirling energy affects the Earth's weather, temperature and atmospheric makeup in numerous ways, some better understood than others.
Lehmacher's project will culminate in the launching of four sounding rockets into the mesosphere and lower thermosphere that will collect data from this volatile region. What Lehmacher and his team learn from these experiments will help enhance the accuracy of our predictions of weather events and patterns.
"Rings of energy that come from major storms near the surface travel upward in the atmosphere as high as 100 kilometers," said Lehmacher, an associate professor in physics and astronomy. "At these incredible speeds, the atmosphere can become unstable. The waves can overturn, like a wave breaking on a seashore. Or they can become unstable from wind shear and cause clear-air turbulence, a similar process as sometimes encountered by aircraft."
This instability causes the upper atmosphere to mix with denser air being cast upward and lighter air downward helping to regulate temperatures around the entire planet.
"This new experiment will use radar and rockets and also an optical instrument to map out an area in the mesosphere about 100 by 200 kilometers, roughly the size of Upstate South Carolina," said Lehmacher, who will launch his rockets from Andoya Space Center in Norway. "The rockets will take off in pairs on two different days. In each pair, one rocket will contain 16 individual measurements of wind, while the other will perform a continuous measurement of wind and temperature."
By sampling and analyzing such a broad area, Lehmacher and his team will seek to gain a clearer understanding of wind movement and the effects of atmospheric buoyancy waves on turbulence.
Members of Lehmacher's atmospheric team include Michael Taylor of Utah State University; Jonathan Snively of Embry-Riddle Aeronautical University in Daytona Beach, Florida; and Franz-Josef Lübken and Jorge Chau of Leibniz-Institute for Atmospheric Physics, Germany.
"Our ultimate goal is to understand the variability of how this 100-kilometer region affects the upper atmosphere through this mixing process," Lehmacher said. "This will help us to better understand how space weather is influenced by tropospheric weather and the many waves emanating from the lower atmosphere."
The Science Mission Directorate Heliophysics Division studies the nature of the sun, and how it influences the very nature of space -- and, in turn, the atmospheres of planets and the technology that exists there. This material is based upon work supported by NASA Heliophysics under Grant Nos. 80NSSC19K0776 and 80NSSC19K0810, respectively. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the view of NASA Heliophysics.
By Jim Melvin