Catching Solar Waves

Uploaded by SpaceRip on 07.06.2011

Everywhere we look in nature, patterns repeat themselves. The curl of a surfing wave, for
example, is mirrored in clouds and on other planets like saturn, and now they've been
spotted in the sun's atmosphere. This shape of wave is often formed by something called
a Kelvin-Helmholtz, or K-H, instability, in which two fluids flow by each other with different
speeds or densities.
For in example in clouds, you have one layer where there is a cloud, and then a higher
layer where you have a jet stream. So at the boundary between these two regions you start
seeing this cloud rolling up. If you look at water waves, the wind will sort-of cause
it to roll-up into a bigger and bigger wave, but eventually this wave will break. This
is very similar to the Kelvin-Helmholtz instability that takes place on the sun, where we have
erupting plasma and we have stationary plasmas.
Spotting a repeating pattern like this is always good news. Since scientists already
know that the movement of the waves transfers energy to the water, they know that the same
thing should be happening in the sun. That extra energy helps explain how the sun's atmosphere,
or corona, heats up to some 1,000 times hotter than the sun's surface. These waves were spotted
in the second coronal mass ejection, or CME, recorded by the Solar Dynamics Observatory
which began looking at the sun in March 2010.
We were able to see as the CME erupted it generated basically a region where the plasma
was evacuated. Since the material from the CME lifted up into space, we see a dark region
that corresponds to the low density region evacuated by the CME and we see just adjacent
to it a brighter region where we have denser plasma. So, now, we see a region where the
vortices start to roll-up.
Astronomers have long thought that turbulence in the corona might help heat it up, but solar
observations still can't see the way the atmosphere moves at small scales. Each of the rolling
surfing waves spotted by SDO was about the size of the United States. And they likely
became more and more turbulent the same way that a breaking water wave froths at its crest.
So it is a way of taking out the energy from the shear flow and converting it, eventually,
into heat. Narrator: Some scientists thought that the sun's powerful magnetic fields would
prevent K-H waves from forming, so the heliophysicists who observed the turbulence on the sun needed
additional evidence.
To support this interpretation, we also developed a model, a computational-numerical model.
We set up this model to resemble what takes place in this region, and we see that, indeed,
this kind of shear can form Kelvin-Helmholtz instability and generate the waves that are
similar to the waves we observe in nature.
A good surfer understands those waves intuitively. Thankfully, scientists understand them physically
too. Watching how they roll around the sun opens the door for more research and better
solar models, helping scientists predict the activity of the star we live with.