Magnetic tornadoes resemble tornadoes on the Earth but have a magnetic
skeleton and are hundreds to thousands times larger in diameter. One such
observed tornado occupies the area equivalent of Europe or the USA.
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Cover page of the edition of Nature published on June
28th, 2012. Credits: Nature Publishing Group
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An international group of researchers from UK, Germany, Sweden, and
Norway has discovered that magnetic tornadoes have swirling speeds of
many
10,000 km/hour. Magnetic tornadoes transport energy from the
Sun's surface into its uppermost layer, the corona, where they contribute to the
heating of the Sun's outer atmosphere. Consequently, magnetic tornadoes may well
be the crucial missing piece of a long-standing puzzle in astrophysics: the
heating of the outer solar and stellar atmospheres.
It is estimated that there are as many as 11,000 of these swirling events
above the Sun's surface at any time.
Professor Robertus Erdelyi
(a.k.a von Fay-Siebenburgen) Head of the Solar Physics and Space Plasma
Research Centre (SP2RC) of the University of Sheffield's School of Mathematics
and Statistics, said:
If we understand how nature heats up magnetised plasmas, like in the
tornadoes observed in the Sun, one day we may be able to use this process to
develop the necessary technology and build devices on Earth that produce
free, clean, green energy. Because of our collaborative research it looks an
essential leap forward is made towards unveiling the secrets about a great
and exciting problem in plasma-astrophysics and we are getting closer and
closer to find a solution.
We report here the discovery of ubiquitous magnetic solar tornadoes and
their signature in the hottest areas of the Sun's atmosphere where the
temperature is a few millions of degree kelvin, about thousands of
kilometres from the Sun's surface. This is a major step in the field.
Professor Robertus Erdelyi added:
One of the major problems in modern astrophysics is why the atmosphere of a
star, like our own Sun, is considerably hotter than its surface. Imagine,
that you climb a mountain, e.g. a monroe in the Scottish highlands, and it
becomes hotter as you go higher and higher. Many scientists are researching
how to "heat" the atmosphere above the surface of the Sun, or any other
star.
The space tornadoes are very magnetic and they operate in plasma - Plasma is
the forth known state of matter, beside solid, liquid and gas and makes
around 99 per cent of the known matter of the Universe. The tornados act in
a similar way to water does if you take the plug out of a full bath.
It
is understood that the energy originates from below the Sun's surface, but
how this massive amount of energy travels up to the solar atmosphere
surrounding it is a mystery. We believe we have found evidence in the form
of rotating magnetic structures - solar tornadoes - that channel the
necessary energy in the form of magnetic waves to heat the magnetised solar
plasma. It is hoped that the process could be replicated here on Earth one
day to energise plasma in tokamak that are believed to be a future device to
produce completely clean energy.
Scientists viewed the solar tornadoes in the outer atmosphere of the Sun,
stretching thousands of miles from the giant star's surface by using both
satellite and ground-based telescopes. They then created 3D-layered seqence of
images of the tornadoes and simulated their evolution with state-of-the-art
numerical codes using the magnetic imprints detected by their high-resolution,
cutting-edge telescopes.
The discovery has been published in the
journal
Nature on June 28th, 2012, and was featured on the
cover page.
Importance of magnetic tornadoes
One would expect that the atmosphere of the Sun should become cooler with
increasing distance from its surface. Remarkably, the opposite occurs and
the temperature rises to over a million degrees. How the atmosphere is
heated to these temperatures is a fundamental question of modern
astrophysics, also referred to as coronal heating problem.
Solving the heating problem is crucial for understanding our Sun, including
the generation of the solar 'wind' and its impact on the Earth's atmosphere
(e.g. solar storms, Northern lights) and spacecraft in Earth's Orbit (e.g.
satellite communication disruption). It is generally believed that large
magnetic arcades that exist in the Sun's outer regions, which are anchored
to the bubbling Sun surface, can transport outwards the energy required for
heating. Scientists have discovered an alternative but widespread way of
transporting enough energy for atmospheric heating due to relentless twisting of the magnetic arcades at
their footpoints. A manifestation of this twisting appears close to the Sun surface and is
described as a 'solar magnetic tornado'.
Frequently asked questions and quotes
- Are these tornadoes on the Sun the same as on Earth?
S. Wedemeyer-Böhm: "In both cases, particles are forced into spirals.
The resulting funnel is narrow at the bottom and widens with height in the
atmosphere. On the other hand, the physical processes behind the formation
of the tornadoes are very different. Tornadoes on the Earth occur in
connection with rotating thunderstorms (or supercells) as a result of
temperature and gas pressure differences and strong shear winds. The solar
tornadoes are generated by rotating magnetic field structures, which force
the plasma, i.e. the ionized gas, to move in spirals."
-
Are these solar tornadoes threatening our Earth?
S. Wedemeyer-Böhm: "No. You may think of these magnetic tornadoes as a local 'weather'
phenomenon on the Sun far away. While they may play an important role for
heating the outer layers of the Sun, magnetic tornadoes do not seem to
have a direct influence on our Earth. A similar effect in large-scale
solar tornadoes (as observed with SDO) may contribute to triggering solar
storms but this hypothesis has yet to be investigated."
-
Are the magnetic tornadoes the same as the solar tornadoes that were
in the news earlier this year?
S. Wedemeyer-Böhm: "The solar tornadoes that have been in the news
earlier this year are much larger than those reported here. The large
tornadoes extend over 100,000 km and more while the magnetic tornadoes
reported here have dimensions of a few 1,000 km. The large tornadoes are
(most likely) caused by rotating solar prominences and may occur in
connection with coronal mass ejections. While they are rather extreme, the
smaller magnetic tornadoes are by far more abundant, which results in a
more basal contribution to the energy balance of our Sun. Both types of
tornado have been observed with SDO."
-
What makes magnetic tornadoes so interesting?
S. Wedemeyer-Böhm: "We demonstrated that magnetic tornadoes channel
energy upwards from the surface of the Sun into its corona. Magnetic
tornadoes constitute thus an important step towards solving the
long-standing coronal heating problem. It is also intriguing that only two
ingredients are needed to generate this phenomenon: 1) magnetic fields and
2) vortex flows that occur in the downdrafts close to the solar surface as a
consequence of the 'bathtub effect'. Both are ubiquitous on the surface of
our Sun, which explains the vast abundance of at least 11,000 magnetic
tornadoes at all times. Their large abundance is a very important finding,
because ubiquity is a necessary condition for a viable mechanism of coronal
heating."
-
Why have solar magnetic tornadoes not been found before?
S. Wedemeyer-Böhm: "These events are rather small details of the Sun.
They are most visible as rotating structures in the chromosphere, the
atmospheric layer between the photosphere (i.e., the "surface") and the
corona above. The chromosphere is very difficult to observe. The discovery
was made possible only now by combining a state-of-the-art ground-based
solar telescope (Swedish 1-m Solar Telescope) with a new solar space
telescope (NASA's Solar Dynamics Observatory), which allow us to see even
small details on our Sun."
-
These tornadoes are so far away. How is it possible to observe
them?
S. Wedemeyer-Böhm: "We used telescopes that can show us small details
of the Sun in high resolution. NASA's space telescope SDO was important for
spotting the imprint of the tornadoes in the corona. The true clue to the
study, however, is the Swedish 1-m Solar Telescope. The high quality images,
which it delivered, made it possible to find the tornadoes in the solar
chromosphere."
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Are the magnetic tornadoes unique for the Sun? Or could exist on other
stars, too?
S. Wedemeyer-Böhm: "It is indeed very likely that magnetic tornadoes
also exist on other stars. The basic ingredients, magnetic fields and vortex
flows at the surface, are probably abundantly present for most stars (as
long as they show convection at the surface).
Chromospheric swirls have first been discovered by Wedemeyer-Böhm & Rouppe
van der Voort in 2008; published in
Astronomy & Astrophysics, 507, L9 - L12.
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Intensity image recorded with the Swedish 1-m Solar Telescope in the
line core of the spectral line of singly ionised calcium (infrared
triplet, wavelength 854.2 nm). The detected chromospheric swirl (dark
ring) is the observational signature of a magnetic
tornado. Credits: Scullion, Wedemeyer-Böhm et al.
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Illustration of an observed magnetic tornado vortex in the solar
atmosphere. The background image was recorded with NASA's Solar
Dynamics Observatory, while the stacked images were obtained with the
Swedish 1-m Solar Telescope (Canary Isl.). The bluish images reveal
the swirl signature of a magnetic tornado. The map of Europe is to
scale. Credits: Scullion & Wedemeyer-Böhm (2012); NASA
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Visualisation of a close-up region in advanced 3D numerical
simulations of a magnetic tornado in the solar atmosphere. The spiral
lines represent the velocity field in the tornado vortex. The images
contain the observed swirl signature (top, bluish) and the Sun's
surface (bottom, reddish). Credits: Wedemeyer-Böhm et al. (2012)
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Visualisation of a close-up region in advanced 3D numerical
simulations of a magnetic tornado in the solar atmosphere. The green
lines represent the velocity field in the tornado vortex, the red
lines represent the magnetic field. The simulated Sun surface is in
grey-scale. Credits: Wedemeyer-Böhm (2012)
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Schematic view of the atmospheric layers of the Sun, the extent of
simulated magnetic tornado, and the resulting net energy
transport. Credits: Wedemeyer-Böhm (2012)
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Visualisation of a close-up region in advanced 3D numerical
simulations. The red mostly vertical lines represent the magnetic
field, whereas the spiral lines represent the streamlines of the
ionized gas in the magnetic tornado. The lower plane shows the
granulation pattern of the solar surface and the magnetic footpoints
(red), whereas the swirl signature (pink ring) can be seen on the
top. Credits: Wedemeyer-Böhm (2012)
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Same as the previous image. Credits: Wedemeyer-Böhm (2012)
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First example of a tornado in a numerical simulation of a cool
star with a surface temperature of 3200 K (compared to the Sun with
5780 K). This unpublished result was presented for the first time at
the 17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun
on June 28th, 2012, in Barcelona, Spain.
Credits: Wedemeyer-Böhm
(2012)
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