Using a combination of ground-based videos and satellite measurements, researchers from the NASA Goddard Space Flight Center have discovered that electrons falling towards the surface of the Earth play a role in forming a type of atmospheric lights known as pulsating auroras.
These pulsating auroras, so named because they regularly appear to flicker on and off, have been observed by humans for several thousands of years. However, scientists are only just now starting to understand what causes this unusual phenomenon.
In the new study, which has been published by the Journal of Geophysical Research, Goddard’s Marilia Samara and her colleagues combined ground-based observations of pulsating auroras and satellite measurements of the quantities and energies of electrons plummeting from the magnetic bubble (magnetosphere) surrounding the Earth to the surface of the planet.
They found that a decrease in the number of low-energy electrons, long believed to have little to no effect on these atmospheric lights, actually corresponded with unusually quick changes in the shape and structure of pulsating auroras. This link would not have been discovered had the team not used both ground and satellite data, Samara said in a statement.
Lower-energy appear to influence these kinds of aurora
While all types of auroras are caused by electrons or another form of energetic particles falling at high speeds into the atmosphere and colliding with atoms and molecules in the air, different types of auroras have electrons from different sources. Active auroras (those that stream across the sky in elongated arcs) occur when a dense wave of solar material hits the magnetosphere.
Conversely, pulsating auroras occur when electrons are sent spinning towards the surface by a series of complicated wave motions in the magnetosphere. These wave motions can take place at any time, and do not necessarily need to be preceded by the impact of a solar material wave.
“The hemispheres are magnetically connected, meaning that any time there is pulsating aurora near the north pole, there is also pulsating aurora near the south pole,” explained Robert Michell, a space physicist at Goddard and co-author of the study. “Electrons are constantly pinging back and forth along this magnetic field line during an aurora event.”
The electrons that travel between the hemispheres are lower-energy secondary electrons, which means that they are slower than those that originally speed in from the magnetosphere. This type of electron is typically flung in all directions following an initial collision from the original, high energy electrons, NASA said, and it’s these particles that influence pulsating auroras.
When observing videos of the atmospheric lights, the research team found that the most distinct changes in their shape and structure occurred when fewer of the secondary electrons were fired back upwards towards the hemispheric magnetic field lines. Based on this discovery, Samara and her colleagues believe that these electrons may play a key role in creating pulsating auroras.
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Feature Image: Thinkstock
Story Image: A time lapse of the pulsating aurora in Alaska. Credit: NASA
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