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

December 18, 2013, University of California, Los Angeles
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: dx.doi.org/10.1038/nature12889

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7 comments

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shavera
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)
shavera
3.3 / 5 (7) Dec 18, 2013
cantdrive85
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.
GuruShabu
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.
Protoplasmix
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?
cantdrive85
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.
alfie_null
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.

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