Mystery Source of Solar Wind Heating Identified

Jul 17, 2009 by Dr. Tony Phillips
The solar wind, shown here in a plot of data from the Ulysses spacecraft, flows away from the sun at a million miles per hour and is heated by a "turbulent cascade." Credit: NASA

(PhysOrg.com) -- The solar wind is hotter than it should be, and for decades researchers have puzzled over the unknown source of energy that heats it. In a paper published in the June 12 issue of Physical Review Letters, NASA scientists say they may have found the answer.

"The energy source is turbulence," says co-author Melvyn Goldstein, chief of the Geospace Physics Laboratory at NASA's Goddard Space Flight Center, Greenbelt, Md. "The sun heats the solar wind by stirring it up."

It's a bit like stirring your coffee--in reverse. When you stir your morning cup of Joe, the coffee cools off. But when the sun stirs the solar wind, the solar wind heats up.

Consider the coffee. When you stir it with a spoon, the stirring produces swirls and vortices in the liquid. The vortices fragment into smaller and smaller eddies until, at the smallest scales, the motions dissipate and the energy turns into heat. Because energy cascades down from the large swirls to the smaller ones, the process is called a turbulent cascade.

Theoretically, the turbulent cascade should heat the coffee. Real coffee cools off, however, because the act of stirring brings warm coffee from the depths of the cup into contact with cooler air above. Cool air absorbs the heat—the heat the coffee had to begin with plus the heat you added by stirring—and you can take a sip without scalding yourself.

But there is no cool air in space, and therein lies the difference between coffee and solar wind.

The sun stirs the solar wind with fast streams of gas that pour out of holes in the sun's atmosphere. Essentially, the solar wind stirs itself. The stirring produces swirls and eddies; larger eddies break into smaller ones, producing a cascade of energy that eventually dissipates as heat. The temperature shoots up and there is no cool air to stop it.

"We've suspected for years that turbulence heats the solar wind," says Fouad Sahraoui, lead author of the paper and a visiting NASA Fellow from the Centre National de la Recherche Scientifique (CNRS) in France. "Now we're getting detailed measurements of the process in action."

The basic concept introduced by physicist Lewis Richardson in 1920. Credit: Antonio Celani

The key data came from a quartet of European spacecraft collectively known as Cluster, launched in 2000 to study the giant bubble of magnetism that surrounds Earth. The magnetosphere protects our planet from solar wind and cosmic rays. It contains the Van Allen radiation belts, auroras, and giant electrical "ring currents" of staggering power. Cluster spends much of its time inside the magnetosphere, where the spacecraft can study the wide variety of phenomena at work there.

One day in March 2006, the four spacecraft took a brief excursion outside the bubble into the solar wind. For three hours, their sensors made rapid-fire measurements of electromagnetic waves and turbulent eddies in the million-kilometer-per-hour gas flowing past them.

"That was when we made the discovery," says Goldstein. "Turbulent energy was cascading from large scale structures around 1,000,000 kilometers (621,400 miles) in size all the way down to structures as small as 3 kilometers (1.8 miles). At the small end of the cascade, energy was absorbed by electrons in the solar wind."

Sahraoui and Goldstein would like to confirm their findings and flesh out the details by sending Cluster back into the solar wind for more than "three lucky hours." But the basic result seems solid enough: Turbulent heating boosts the temperature of the solar wind near Earth from tens of thousands of degrees (the value theoreticians expect) to hundreds of thousands or more.

Goldstein says such turbulent heating probably happens in many other astrophysical situations, from stellar winds to planetary magnetospheres to black holes. There's even a down-to-Earth application: nuclear fusion reactors. Turbulence inside experimental fusion chambers can produce instabilities that destroy the confinement of the fusion plasma.

"The is a natural laboratory for understanding this physics," says Sahraoui, "and we are planning more observations to see how common the phenomenon might be."

Provided by JPL/NASA (news : .gov/index.cfm" target="_blank">web)

Explore further: IHEP in China has ambitions for Higgs factory

add to favorites email to friend print save as pdf

Related Stories

Team discovers 'throttle' for solar wind

May 17, 2007

Helium may act as a "throttle" for the solar wind, setting its minimum speed, according to new results from an MIT-led team using NASA's Wind spacecraft.

Physicists Trash Turbulence Lab

Apr 13, 2005

Researchers at the University of Warwick have trashed the world's biggest turbulence lab by turning a pleasant stream into a raging torrent - but they say their actions will lead new understandings in one of the main unsolved ...

Recommended for you

Chemist develops X-ray vision for quality assurance

2 hours ago

It is seldom sufficient to read the declaration of contents if you need to know precisely what substances a product contains. In fact, to do this you need to be a highly skilled chemist or to have genuine ...

The future of ultrashort laser pulses

2 hours ago

Rapid advances in techniques for the creation of ultra-short laser pulses promise to boost our knowledge of electron motions to an unprecedented level.

IHEP in China has ambitions for Higgs factory

19 hours ago

Who will lay claim to having the world's largest particle smasher?. Could China become the collider capital of the world? Questions tease answers, following a news story in Nature on Tuesday. Proposals for ...

The physics of lead guitar playing

21 hours ago

String bends, tapping, vibrato and whammy bars are all techniques that add to the distinctiveness of a lead guitarist's sound, whether it's Clapton, Hendrix, or BB King.

The birth of topological spintronics

22 hours ago

The discovery of a new material combination that could lead to a more efficient approach to computer memory and logic will be described in the journal Nature on July 24, 2014. The research, led by Penn S ...

User comments : 14

Adjust slider to filter visible comments by rank

Display comments: newest first

E_L_Earnhardt
1 / 5 (1) Jul 17, 2009
E=MC2 The basic electron is invisable, (except by its shadow when it absorbs energy.) It contains energy when in motion, (spin or vector). It has mass when in motion. It expresses its energy when its vector is changed. IE "The electron IS Energy"!
brant
2.6 / 5 (5) Jul 17, 2009
Baloney. This is a terrible article. Where does the energy come from????



"The energy source is turbulence," is complete BS.



Turbulence is an energy sink.



An accelerated particle is a hot particle. Turbulence slows things down.
KBK
2.3 / 5 (3) Jul 18, 2009
Electric Universe.
omatumr
1 / 5 (2) Jul 18, 2009
"HOTTER THAN IT SHOULD BE"?

That attitude says a lot about the problem.

Let's focus on "what is" and ask:

a.) What produces the turbulence?

b.) What accelerates the "fast streams of gas that pour out of holes in the sun's atmosphere"?

c.) Are these the same H ions that are accelerated upward by deep-seated magnetic fields, maintaining mass separation in the sun, and producing sun spots when they protrude through the visible solar "surface"?

The solar wind is exactly as hot as it should be for the sun as it really is.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
JukriS
1 / 5 (3) Jul 18, 2009
When you blow an insane campfire, campfire gets hot!

Energy From outside can get Sun by the fire burning up.

Waves of energy coming to Sun all a time.

Sometimes there mide coming some strong energypulse and next one coming after 11 years etc.

Sometimes coming some very strong energypulse and next one after 10 000 years or maybe after millions years!

http://onesimplep....com/296

.

Velanarris
5 / 5 (1) Jul 18, 2009
Baloney. This is a terrible article. Where does the energy come from????

"The energy source is turbulence," is complete BS.

Turbulence is an energy sink.

An accelerated particle is a hot particle. Turbulence slows things down.

Turbulence increases friction, which in turn increases energy release.
Torbjorn_Larsson_OM
4.5 / 5 (4) Jul 18, 2009
""The energy source is turbulence," is complete BS."

No, the article is quite clear that it is the fragmentation of the solar wind that is responsible (by way of turbulence), not a steady state flow.

"The solar wind is exactly as hot as it should be for the sun as it really is."

I'm not sure what you mean by "as it really is". Solar surface temperature as it really is, is easily measured to ~ 6*10^3 K. That is magnitudes lesser than solar wind temperatures mentioned above.

Even if the effective temperature is set in large by the wind accelerated by the Sun average E & M fields in the solar atmosphere, this effect may be short of what is measured. What the research presumably does is to explain the discrepancy.
regnevacs
not rated yet Jul 19, 2009
cosmic rays are hitting the earth and some are going right through it so the magnetosphere isn't doing its job!
earls
not rated yet Jul 19, 2009
So what creates the turbulence? I mean, space is a near vacuum, so it's not like the wind is blowing the candle.

Hot gas rises which becomes turbulent, interfering with itself, then rises faster as it fragments? An exchange of volume for velocity?
Velanarris
not rated yet Jul 20, 2009
So what creates the turbulence? I mean, space is a near vacuum, so it's not like the wind is blowing the candle.

Hot gas rises which becomes turbulent, interfering with itself, then rises faster as it fragments? An exchange of volume for velocity?


The intrasolar medium is far from a vaccuum. I hate the fact they taught that in high school science. The turbulence is caused by many things, cosmic radiation, the magnetospheres, atmospheres, gravity, and electric fields of the planets, the constant rotation of the Milky Way, outer gasses slowing down as their energy has been emitted being hit from behind by more energetic particles, etc.
omatumr
1 / 5 (3) Jul 20, 2009
BRANT IS EXACTLY RIGHT

Baloney. This is a terrible article. Where does the energy come from????

"The energy source is turbulence," is complete BS.

Turbulence is an energy sink.

An accelerated particle is a hot particle. Turbulence slows things down.


Thanks, Brant! Keep telling it like it is.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
Velanarris
not rated yet Jul 20, 2009
Thanks, Brant! Keep telling it like it is.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
That's very far from "how it is", and I'm quite frankly surprised by your statement.
superhuman
5 / 5 (2) Jul 30, 2009
"The energy source is turbulence,"

Turbulence is NOT an energy source, this is a nonsensical statement. Turbulence only changes how energy is distributed among interacting particles but the energy has to be there to begin with.
Velanarris
5 / 5 (1) Jul 30, 2009
"The energy source is turbulence,"


Turbulence is NOT an energy source, this is a nonsensical statement. Turbulence only changes how energy is distributed among interacting particles but the energy has to be there to begin with.

And this is the correct way to frame it. Turbulence does not "create" energy. It distributes released energy. So if you want to know where the energy is comming from follow the solar wind.

The solar wind exits the sun energized by the energy released during solar fusion. These energized particles exit at a high energy or velocity and begiin encountering resistance provided by the ambient molecules and particles inhabiting intrasolar space. This resistance results in bumping, rubbing, etc which is friction. On contact and exposure to friction (some particles must escape with no physical interaction according to probability) these particle transmit some of their energy to the local particles thus losing their individual energy but diffusing their energy into the rest of the system. On a broad scale this would appear to be "heating" of the solar wind as opposed to having a heterogenous soup of particles with wildly mismatched energy.

So does it make more sense when they improperly state "turbulence is the cause of the heating"?

It is the cause of the heating, but the source of the energy is fusion.