As a large windstorm descends over a mountain range, leaves shake from their branches, dust and dirt scatter amongst the trees, and the valleys moan as the wind whips between the high peaks. And all the while, gravity waves are created in our atmosphere.
Atmospheric gravity waves—created by irregularities in fluid-like motion, such as wind flow over topography—play an important role in the energy budget of Earth’s thermosphere. This layer in the upper atmosphere, which is home to low-orbit satellites and the International Space Station, is strongly influenced by solar activity; its temperature can fluctuate by 500°C when the Sun is very active. Because direct measurements of gravity waves are exceedingly rare, numerical modeling is the best source of information that scientists currently have to understand the influence of gravity waves on the thermosphere. Now, NASA has funded a new instrument package, the Occultation Wave Limb Sounder (OWLS), to help change that.
OWLS will consist of two instruments to be built by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder: the Extreme Ultraviolet Occultation Photometers (EUV-OP) and the Compact Spectrograph for Occultations on Limb (CSOL). These instruments will address the gaps in our understanding regarding the influence that gravity waves have on the thermosphere’s temperature. The results will be used to infer atmospheric properties such as temperature and density and how they vary with gravity wave energy and momentum flux.
“I’m looking forward to answering the seemingly basic question of how gravity waves affect the temperature of the uppermost region of Earth’s atmosphere,” says Ed Thiemann, a LASP research scientist and the OWLS principal investigator (PI). “Gravity waves are fascinating because they provide a pathway for the weather that we are all familiar with to significantly impact what is commonly considered outer space.”
How does a rainstorm affect satellites?
OWLS will fly on the third satellite of the International Satellite Program in Research and Education (INSPIRESat-3). This microsatellite, to be built by the Nanyang Technological University (NTU) in Singapore, will be launched into a polar orbit by the Indian Space Research Organization in 2024. NTU will lead INSPIRESat-3 mission operations, and LASP will head OWLS’ instrument operations and the processing of all the science data.
“It’s mind-blowing to think that storms over the Pacific could in any way impact astronauts on the International Space Station, but those are the distances over which gravity waves can have an influence,” Thiemann says. “For the first time, the OWLS measurements will quantify the magnitude of this influence, be it large or small, and provide a benchmark for current and future theories to be tested against it.”
Because the region of the atmosphere that OWLS will be studying encompasses Low Earth Orbit, where thousands of satellites are located, understanding how gravity waves affect this space should ultimately improve the forecasting of satellites’ orbital trajectories, allowing us to predict and mitigate impacts, says LASP researcher Katelynn Greer, the Science PI of OWLS. This danger was highlighted by the recent Russian anti-satellite test, which resulted in a large space debris field that forced astronauts on the International Space Station to undertake emergency procedures for safety.
Since gravity waves are present to some degree in all except the thinnest atmospheres in our solar system, Thiemann believes the OWLS’ measurements will have important implications that extend well beyond Earth orbit. “Understanding the basic processes and characteristics of gravity waves here at Earth,” he says, “will bring us one tiny step closer to understanding the universe around us.”