Thomas R. O'Donnell

Roundup: Van Allen belts give electrons a jolt, a super scanner and a flood study dries up

In Uncategorized, University research on August 26, 2013 at 5:00 am
Van Allen belts with graph of electron acceleration

Recent observations by NASA’s twin Van Allen Probes show that a local kick of energy accelerates particles in the radiation belts surrounding Earth. The readings help explain how these particles reach energies of 99 percent the speed of light. Image Credit: G. Reeves/M. Henderson

I was in knee pants when I first heard about the Van Allen radiation belts, the donut-shaped rings of charged particles circling the Earth. In the movie (and later television series), “Voyage to the Bottom of the Sea” the belts catch fire, threatening the planet with global warming at hyperspeed – an impossible apocalypse.

The belts were new and little explored then, and one of my siblings told me they were named for their discoverer, James Van Allen, a University of Iowa physicist and a born and bred Iowan. In typical chip-on-the-shoulder Iowa fashion (“Hey, we’re more than corn! We have scientists!”), I’ve been proud of that discovery and its name ever since.

Van Allen’s research brought prestige and fame to U of I’s physics department and attracted some top scientists. And almost 60 years after the belts’ discovery, the university’s research still yields new insights.

The latest, published last month, shows the belts act as a potent particle accelerator, pushing electrons to nearly light speed.

The research was published online July 25 (full text is paywalled) on Science Express, one of the arms of the prestigious journal Science. Craig Kletzing and William Kurth with the U of I Department of Physics and Astronomy were part of a team that included lead author Geoffrey Reeves of Los Alamos National Laboratory and others from the universities of New Hampshire, Colorado and California, NASA Goddard Space Flight Center, and Aerospace Corp.

Van Allen Probes deploy their solar arrays in this artist's conception.

This NASA artist’s conception shows the identical Van Allen probes as they follow similar orbits, taking them through both the inner and outer radiation belts. The highly elliptical paths carry the probes from a minimum altitude of about 373 miles (600 kilometers) to a maximum altitude of approximately 23,000 miles (37,000 kilometers).

The study relies on data from a pair of satellites, the Van Allen Probes, which orbit Earth at altitudes ranging from 300 miles to as much as 25,000 miles, passing directly through the radiation belts. The probes carry a U of I-designed instrument, the Electric and Magnetic Field Instrument Suite with Integrated Science.

One mystery researchers hoped to resolve is what accelerates electrons, found in outer regions of the Van Allen belts, to 99 percent of light speed. With that amount of energy, these electrons can penetrate most satellite shielding.

The probes were launched in August 2012 and the researchers got an October surprise. The satellites detected a spike in the energy of electrons in the outer belt – an increase of nearly 1,000 times over a span of only about 12 hours. Just a week before, instruments showed electron energies were weakening.

That told scientists the energy burst came from within the belts. Meanwhile, other readings contradicted an alternative explanation, that a source outside the belts accelerates the electrons.

In the U of I release, Kletzing provides a neat analogy for how physicists spotted the difference. He compared it to how someone can tell whether a perfumed woman is in a doorway or the middle of a room:

“If the woman is in the doorway, then you should detect a decline in the intensity of the fragrance as you move away from the door,” Kletzing says. “But if she is in the middle of the room, then the scent will be strongest inside the room, decreasing in all directions away from where she is standing.”

This is rather sexist. Why not a fat guy with B.O.? Nonetheless, the idea conveys how the probes could identify the source by detecting accelerated electrons.

Meanwhile, Ames Laboratory is getting a new science toy: a high-tech relative to the magnetic resonance imaging (MRI) scanners hospitals use to get detailed pictures of our innards.

DNP-NMR scanner like the one Ames Laboratory will acquire.

A DNP-NMR scanner from Bruker Corp., similar to one the Ames Laboratory will acquire. Credit: Bruker Corp.

The instrument Ames Lab will install next year combines nuclear magnetic resonance (NMR), the basic principle behind the MRI, with dynamic nuclear polarization (DNP), which uses microwaves to polarize electrons and boost the NMR response. An Ames Lab release says the hypersensitive DNP-NMR spectrometer will be the first of its kind in the United States to focus on materials and materials chemistry – the Department of Energy facility’s specialty.

Lab researchers will use the instrument to get more intricate data on new materials important to things like energy storage, chemical processing and nanoscale structures.

Finally, earlier this month NASA researchers issued a follow-up to their Global Precipitation Measurement mission in eastern Iowa. When I wrote about this in June, the researchers were tracking heavy rain and potential floods. In fact, just a couple days after I posted about their work they watched a line of heavy thunderstorms and tornadoes pass nearby.

It was a perfect spring to gather data designed to validate and interpret satellite measurements. But when the NASA radar units left in mid-June, they seemed to take the rain with them. Now Iowa struggles with a drastic dry spell.

NASA and Iowa Flood Center researchers will crunch the data, but the release says early results suggest broad agreement between ground instruments and satellites. Ultimately, the idea is to improve models so they better predict floods and droughts. This nifty NASA video lays out the case.

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