It’s long been believed that all the energy affecting Earth’s uppermost atmosphere solely comes down from the sun. USU researchers, Mike Taylor and Dominique Pautet’s, study of gravity waves suggests otherwise. Some of the solar energy that reaches the ground can be transmitted back upwards, shaping the weather and climate above Earth.
Not to be confused with the gravitational waves of Einstein’s Theory of Relativity, gravity waves occur in fluid mediums of different densities such as in water and the atmosphere. When these mediums are disturbed, gravity acts upon them to return them to a stable state. As a result, oscillations of energy propagate outwards as waves. Drop a stone in a pond. The mesmerizing ripples that result, growing wider and wider, are visible evidence of this phenomenon.
You can’t see the gravity waves studied by Taylor and Pautet, at least not with the naked eye. This research duo utilizes infrared imaging to look at waves in the third layer of the Earth’s atmosphere, the mesosphere, 30 to 50 miles up.
“What happened was that Kodak made infrared film available and that made possible long exposure pictures. Up until then you had a very sophisticated devices to see anything in the infrared” Taylor said. “It’s the technology that opens up the possibilities.”
Taylor arrived at Utah State in 1999. At the time his cameras were only capable of seeing the waves, so he partnered with researchers who operate lidar instruments at the Bear Lake Observatory. Unlike his camera that takes images horizontally at one altitude giving insights to wave properties, lidar collects data from a single point vertically to measure characteristics such as temperature and brightness of the surrounding environment.
After finishing his doctorate Pautet joined Taylor in 2001. Since, they’ve installed ten cameras at different latitudes around the globe, including at the Arctic Lidar Observatory for Meteorological and Atmospheric Research (ALOMAR) facility in Norway. The sensitivity of their cameras allows them to see the gravity waves despite the interference of the northern lights.
Waves in the upper atmosphere may seem abstract, but their existence is felt at ground level in the weather. Thunderstorms, weather fronts, wind patterns, large explosions, volcanic eruptions, even earthquakes all disrupt the equilibrium of the atmosphere, sending energy waves rippling outward and upward like that stone dropped in water. The weather and climate of our upper atmosphere plays an important role in weather predictions at ground level, long term climate modeling and in the possibility of high atmospheric flight.
A recent finding has surprised both Taylor and Pautet; small disturbance on the ground can create significant turbulence in the mesosphere.
Discovered during a recent experiment called Gulf Stream Five, Taylor and Pautet put three of their cameras on an airplane and flew over the mountains of New Zealand. After seeing this disturbance in the gravity waves, the pair got adventurous. The crew flew over two small islands in the Southern Sea off the coast of Antarctica. No taller than 600 meters, this minor disturbance created really large waves.
This is due to the decrease in the atmosphere’s density as elevation increase. The thinner the atmosphere becomes the greater the change the energy in these waves has on the surrounding environment.
“It is like if you walked in mud towards a lake,” Pautet said. “At first the mud would rise slowly with your feet, but as you walked closer to the lake, there would be more and more water mixing with the mud and you could move faster and create a bigger splash.”
Gravity waves continue moving upwards until interrupted by winds or until the atmosphere gets so thin that they can no longer move forward, breaking and leaving energy deposits that, like waves crashing on the beach and shape the shore, shape the background temperature and winds of the atmosphere.
“Basically it means that small weather disturbance can affect the upper atmosphere and that explains why we can see these waves everywhere,” Taylor said. “When I first came here a long time ago we had the sensitivity of just seeing the brightest waves, now we can see even the really faint ones. We can see that the whole atmosphere is just churning with these waves. We are at the stage of quantifying their impact on the atmosphere at all levels.”