Scientists solve a decades-old mystery in the Earth's upper atmosphere

Dec 18, 2013
The top panel shows electron fluxes before (left) and after (right) a geomagnetic storm. The injection of low-energy plasma sheet electrons into the inner magnetosphere (1) causes chorus wave excitation in the low-density region outside the cold plasmasphere (2). Local energy diffusion associated with wave scattering leads to the development of strongly enhanced phase space density just outside the plasmapause (3). Subsequently, radial diffusion can redistribute the accelerated electrons inwards or outwards from the developing peak (4). Credit: Jacob Bortnik/UCLA

New research published in the journal Nature resolves decades of scientific controversy over the origin of the extremely energetic particles known as ultra-relativistic electrons in the Earth's near-space environment and is likely to influence our understanding of planetary magnetospheres throughout the universe.

Discovering the processes that control the formation and ultimate loss of these electrons in the Van Allen radiation belts—the rings of highly charged particles that encircle the Earth at a range of about 1,000 to 50,000 kilometers above the planet's surface—is a primary science objective of the recently launched NASA Van Allen Probes mission. Understanding these mechanisms has important practical applications, because the enormous amounts of radiation trapped within the belts can pose a significant hazard to satellites and spacecraft, as well astronauts performing activities outside a craft.

Ultra-relativistic electrons in the Earth's outer radiation belt can exhibit pronounced variability in response to activity on the sun and changes in the solar wind, but the dominant physical mechanism responsible for radiation-belt electron acceleration has remained unresolved for decades. Two primary candidates for this acceleration have been "inward radial diffusive transport" and "local stochastic acceleration" by very low-frequency plasma waves.

In research published Dec. 19 in Nature, lead author Richard Thorne, a distinguished professor of atmospheric and oceanic sciences in the UCLA College of Letters and Science, and his colleagues report on high-resolution satellite measurements of high-energy electrons during a geomagnetic storm on Oct. 9, 2012, which they have numerically modeled using a newly developed data-driven global wave model.

Their analysis reveals that scattering by intense, natural very low–frequency radio waves known as "chorus" in the Earth's upper atmosphere is primarily responsible for the observed relativistic electron build-up.

The team's detailed modeling, together with previous observations of peaks in electron phase space density reported earlier this year by Geoff Reeves and colleagues in the journal Science, demonstrates the remarkable efficiency of natural wave acceleration in the Earth's near-space environment and shows that radial diffusion was not responsible for the observed acceleration during this storm, Thorne said.

This is a graphic depiction of NASA's Van Allen Probes orbiting within Earth's radiation belts. Credit: NASA

Co-authors of the new research include Qianli Ma, a graduate student who works in Thorne's lab; Wen Li, Binbin Ni and Jacob Bortnik, researchers in Thorne's lab; and members of the science teams on the Van Allen Probes, including Harlan Spence of the University of New Hampshire (principal investigator for RBSP-ECT) and Craig Kletzing of the University of Iowa (principal investigator for EMFISIS).

The local wave-acceleration process is a "universal physical process" and should also be effective in the magnetospheres of Jupiter, Saturn and other magnetized plasma environments in the cosmos, Thorne said. He thinks the new results from the detailed analysis of Earth will influence future modeling of other planetary magnetospheres.

The Van Allen radiation belts were discovered in the Earth's upper atmosphere in 1958 by a team led by space scientist James Van Allen.

Explore further: How did a third radiation belt appear in the Earth's upper atmosphere?

More information: Paper:

Related Stories

Van Allen Probes pinpoint driver of speeding electrons

Jul 25, 2013

Researchers believe they have solved a lingering mystery about how electrons within Earth's radiation belt can suddenly become energetic enough to kill orbiting satellites. Thanks to data gathered from an ...

Recommended for you

Astronauts to reveal sobering data on asteroid impacts

6 hours ago

This Earth Day, Tuesday, April 22, three former NASA astronauts will present new evidence that our planet has experienced many more large-scale asteroid impacts over the past decade than previously thought… ...

Rosetta instrument commissioning continues

7 hours ago

We're now in week four of six dedicated to commissioning Rosetta's science instruments after the long hibernation period, with the majority now having completed at least a first initial switch on.

Astronaut salary

7 hours ago

Talk about a high-flying career! Being a government astronaut means you have the chance to go into space and take part in some neat projects—such as going on spacewalks, moving robotic arms and doing science ...

Red moon at night; stargazer's delight

Apr 16, 2014

Monday night's lunar eclipse proved just as delightful as expected to those able to view it. On the East Coast, cloudy skies may have gotten in the way, but at the National Science Foundation's National Optical ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

3.7 / 5 (9) Dec 18, 2013
Hurr durr astrophysicists don't know anything about plasmas. It's almost like they can't drive themselves to school or something. (in b4 crackpottery)
3.3 / 5 (7) Dec 18, 2013
1.9 / 5 (9) Dec 18, 2013
Hurr durr astrophysicists don't know anything about plasmas. It's almost like they can't drive themselves to school or something. (in b4 crackpottery)

You got that right, this abortion above doesn't change Alfven's assessment one bit.
1.6 / 5 (7) Dec 18, 2013
You two got it right!
Unfortunately, soon some will come here and put an "1" on anyone talking about plasma as it is something taboo or (more arrogantly) "not belonging to the main stream of the sacred physics" that is behaving as the Santa Inquisición, presently.
Frankly, I do not understand why such a resistance to the amazing plasma physics so well presented and developed by Afven.
5 / 5 (8) Dec 19, 2013
Frankly, I do not understand why such a resistance to the amazing plasma physics so well presented and developed by Afven.

Because you say things like, "astrophysicists don't know anything about plasmas." A statement like that is likely to elicit a reaction that's more akin to flat-out rejection rather than just resistance. But the main reason you observe "such a resistance" is because you don't understand what it is that the astrophysicists *do* know about plasmas, astrophysics, cosmology, and the many relevant theories and extensions. When you refer to, "the above abortion," you've persuaded no one to see it as such; rather, you've shown that you don't fully understand the subject matter. Oh, and a puppet is only as smart as the puppeteer. The puppet dances the same dance, walks the same walk, and talks the same talk. And crap by any other name, reeks the same. See what you instead inspire?
1 / 5 (7) Dec 19, 2013
When astrophysicists start using the particle/circuit models developed by men like Alfven et al. then my statements will be wrong. Until then, by their use of ideal MHD models, they will have an incomplete grasp on the properties of plasma. That is to say, I know exactly what they *do not* know about plasma by the use of the incorrect models. Things such and instabilities, double layers, currents, and the need to understand the tremendous complexity of a spinning charged sphere (Earth) orbiting in the Sun's electrified plasma environment within an electric field. If they want to know more about near earth electrons they need to step back and understand the Sun-Earth better. Experimentation is a start, Kristian Birkeland predicted the Van Allen belts 60 years before the discovery due to his Terrella experiments.

BTW, I wouldn't be able to keep up with sock puppets, although I appreciate the allegation. All of my accounts, xbox, ps3, yahoo, EU, Phys, goog, etc..., all the same.
5 / 5 (4) Dec 19, 2013
Apologies for being off-topic, but the second comment above, by shavera, is a measure of how the rating system works with robots. As I write this, it's at 3.7 - for an empty entry.
no fate
2 / 5 (4) Dec 19, 2013
"But the main reason you observe "such a resistance" is because you don't understand what it is that the astrophysicists *do* know about plasmas, astrophysics, cosmology, and the many relevant theories and extensions."

Mainstream models are still based on gravity, as a descriptor of reality they fail miserably unless adjusted, bolstered and tweaked with hitherto undetectable agents. Below is a good paper on Stochastic acceleration.


The Stochastic process, specifically the turbulence at the boundary of interacting magnetic fields is the culprit (not too keen on the "plasma wave" mechanism) as mentioned in the article. It's how you (mainstream) see something like the suns equatorial super rotation and apply a different process that is mind boggling. Any observed differences are due to plasma density and magnetic field strength.

More news stories

Cosmologists weigh cosmic filaments and voids

( —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Hubble image: A cross-section of the universe

An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range ...

Hackathon team's GoogolPlex gives Siri extra powers

( —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...