23 April 2019
By Liza Lester
A new study fills in gaps in a long-running mystery of what causes “speed bumps” in space that slow satellites in orbit.
Using new data from the Rocket Experiment for Neutral Upwelling 2 (RENU2) mission, the new study in AGU’s journal Geophysical Research Letters finds a type of high-altitude aurora are responsible, at least in part, for moving pockets of air high into the atmosphere where they can cause drag on passing satellites.
The aurora seen dancing in this video through the glass bubble of Kjell Henrikson Observatory in Svalbard are not the typical bright ribbons of light seen at night in Earth’s high latitudes. Known as Poleward Moving Auroral Forms (PMAF), they are less energetic, and though they can be seen from the ground, the observer needs a very dark location to catch a glimpse.
PMAF are dim and distant. But because they occur at such high altitudes, these lower-energy auroras transfer more of their energy to the thin atmosphere at 250-400 kilometers (150-250 miles) above the ground, and produce more interesting effects than more familiar aurora, which sparkle at closer to 100 kilometers (60 miles) up.
When early space programs first put satellites into orbit, they noticed degradation of the satellites’ orbits when the sun was active. Something was creating drag on the satellites, like driving a car into a strong headwind. This is a problem, because when the extra drag slows the satellites down, they move closer to Earth. Without extra fuel to boost them back up to speed, they will eventually fall back to Earth.
Scientists developed a hypothesis that air from lower in Earth’s atmosphere was welling up into the normally wispy upper reaches of the atmosphere and dragging on satellites in low Earth orbit. In the early 2000s, new data showed some of the upwelling that occurs within these “space speed bumps” consists of sharp, intense spikes.
Marc Lessard, a physicist at the University of New Hampshire and lead author of the new study, and his colleagues began to suspect that aurora may be instigating the upwelling events, because poleward moving auroral forms seemed to be coincidentally present at the right time. To find out, they needed a closer look at the development of the speed bumps.
RENU2 lifted off from Svalbard on the day this video was captured, carrying instruments up into an upwelling event to measure it in action. The new study found that repeated passes of poleward moving auroral arcs injected enough energy to produce the upwelling of air from up to several hundred kilometers lower in Earth’s atmosphere. RENU2 observed a more complex structure to the upwelling events than expected, more like the rising bubbles of a lava lamp than a smooth wave.
The video was taken by Fred Signernes looking straight up through a glass dome at Kjell Henrikson Observatory in Svalbard. A shadowy figure clears the glass of snow and ice (with the help of a little Rasputin vodka) to reveal the dance of the poleward moving auroral forms.
Liza Lester is a senior public information specialist and writer at AGU. Follow her on twitter at @lizalester.
Video Credit: Fred Sigernes/Kjell Henrikson Observatory.