Nitric oxide in the upper atmosphere
Nitric oxide (NO) is created when the aurora interacts with the upper atmosphere. Streams of highly energetic electrons in the aurora tear apart molecules such as nitrogen. When nitrogen bonds break, the atoms interact with molecular oxygen to form nitric oxide.
If the gas moves down into the stratosphere, it destroys ozone. "Even a small reduction in ozone can affect upper atmospheric winds and potentially change global temperature profiles," said Bailey.
During the last 10 years, there were several winters where atmospheric scientists observed plumes of nitric oxide—assumed to originate from auroral interactions—descend and begin to eat away at the ozone layer, said Bailey.
"We're not sure why these descent events are happening now and never before," said Bailey. "It's possible that they were occurring, and our instruments are finally precise enough to detect them, but they could also signify a change in the atmosphere."
Sunlight destroys nitric oxide molecules in less than a day, making them difficult to study. However, in the polar night, nitric oxide abundances can grow large.
"We needed a technique to make direct measurements in the polar night," said Bailey.
Bailey, along with co-principal investigator William McClintock from the University of Colorado, Justin Carstens, a research associate, and Karthik Venkataramani, a Ph.D. student, set out to measure nitric oxide accumulation during the 24-hour darkness of the Arctic winter.
On January 27, after a month of intense preparation in temperatures that plunged to 50 below zero, the Polar Night Nitric Oxide (PolarNOx) experiment was launched on a NASA sounding rocket from the Poker Flat Research Range in Alaska.
As the rocket climbed to an altitude of 176 miles, its sensors locked onto Algenib, a star located deep in the polar night that was chosen because it shines relatively brightly in the ultraviolet spectrum that nitric oxide absorbs.
During the eight-minute journey, a spectrograph measured the starlight as it passed through nitric oxide molecules in the atmosphere.
Nitric oxide molecules absorb photons in distinct frequencies, which can be seen in the electromagnetic spectrum of the gas. By analyzing the spectrum, researchers can identify and study the temperature and number density profile of nitric oxide.
Analyzing the results
Thanks to the data collected by PolarNOx, Bailey's team will begin analysis. After they correct the data to account for the motion of the rocket—a slow process requiring that they treat each second of data differently—they will transform it into a profile of nitric oxide as a function of height.
"This is not a new technique—it's been done for other atmospheric gases, including ozone," said Bailey. "But it's the first time anyone has used it to study nitric oxide."
And it won't be the last time. Now that they know the technique works, Bailey and his team can use it in the future to study nitric oxide's variability.