(CN) – Scientists have found the mechanism behind an abrupt and drastic phenomenon that can swing temperatures in Earth’s upper atmosphere by more than 1,000 degrees Fahrenheit, acting as a “natural thermostat” that cools down air heated by violent solar activity.
The team identified the formation of a trace chemical, nitric oxide, from coronal mass ejections (CMEs) and solar flares that pour energy into Earth’s atmosphere.
CMEs speed toward Earth at more than 1 million miles per hour, creating shock waves – similar to how supersonic aircraft create sonic booms – that expand and heat up the atmosphere. But such heating is followed by a rapid cooling, the cause of which had escaped scientists – until now.
“What’s new is that we have determined the circumstances under which the upper atmosphere goes into this almost overcooling mode following significant heating,” said co-author Delores Knipp, a professor at the University of Colorado at Boulder’s department of aerospace engineering sciences. “It’s a bit like having a stuck thermostat – it’s really a case of nature reining itself in.”
Solar storms can produce dramatic temperature changes in the upper atmosphere, including the ionosphere, which ranges from about 30 miles in altitude to the edge of space about 600 miles above sea level. CME material slamming into Earth’s atmosphere can spike temperatures by up to 750 degrees Fahrenheit, before the formation of nitric oxide created by the energy infusion quickly cools things by about 930 degrees Fahrenheit, according to Knipp.
Knipp was able to identify the mysterious mechanism after reviewing satellite data from a massive solar storm that pounded Earth in 1967. After reviewing a graphic depicting the storm, featured in a long-forgotten manuscript, Knipp looked at more recent satellite datasets and eventually connected the CMEs to the formation of nitric oxide.
“We found that the fastest material streaming off the sun was triggering these shockwaves, causing the atmosphere to heave up and heat up,” she said. “But it became very clear that these shock waves were at the root of creating the nitric oxide, which cause the atmosphere to shed energy and cool.”
The team reviewed data collected by the Sounding of the Atmosphere using the Broadband Emission Radiometry, or SABER, instrument on NASA’s TIMED satellite. SABER has been collecting data on nitric oxide in the atmosphere since its launch in 2001.
SABER followed the launch of the Student Nitric Oxide Explorer (SNOE), a nitric oxide-measuring satellite that involved more than 100 primarily undergraduate students from University of Colorado at Boulder in its design and construction. Once in orbit, SNOE was controlled by students on the university’s campus 24 hours a day for almost six years.