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Aug. 04, 2011

Solar Corona Mystery Explained?

by April Garbuz

Click to enlarge images

By April Garbuz, Wilton High School

I spoke with Scott McIntosh, a scientist at NCAR's High Altitude Observatory, about his study, published in the July 28 issue of the journal Nature, that suggests magnetic waves are responsible for making the Sun's outer atmosphere (corona) 20 times hotter than its surface. This research can take scientists closer to understanding the solar cycle and the Sun's impacts on Earth.

A satellite-derived image, looking down on a layer of the Sun's atmosphere, or corona. Photo credit: UCAR

How your study was conducted?
Our study was conducted using the high temporal and spatial resolution of the Solar Dynamics Observatory.

[The Solar Dynamics Observatory (SDO) takes a closer look at the Sun. SDO will help us understand where the Sun's energy comes from, how the inside of the Sun works, and how energy is stored and released in the Sun's atmosphere.]

With the Hinode spacecraft in 2007, we had a sniff of what was going on, but we did not have the coronal observations to prove that the large wave flux was visible in the corona. We were salivating at the opportunity when SDO was switched on. We still had to use some image processing to pull the wave motions out of the coronal images, but those are fairly straightforward.

What do the satellite observations reveal?
The entire solar corona is wiggling like a blob of jelly. It is really obvious. In fact, we can demonstrate that a LOT of wave energy is visible in coronal emission -- therefore it makes it into the corona without being significantly reflected. The waves, after being overlooked for many years as a viable coronal heater, they are back in the game.

What is the role of Alfvén waves?
Alfvén waves travel on magnetic field lines and transfer information from one place to another, just like a sound wave carries information from one hilltop to another. The medium, though, is not air but a magnetic field line. The Alfvén waves are most likely triggered by the bubbling and rolling of the lower solar atmosphere -- think of the ocean -- they then travel upward into the upper atmosphere carrying a little bit of that convective energy.

Why are geomagnetic storms significant?
Geomagnetic storms have the potential to significantly affect our increasingly technological civilization through damage to electrical grids, communication, and navigation satellites.

What does the study show us about how energy and mass move through the Sun's outer atmosphere?
Combined with our study in January (performed with a different "look" at the same dataset) we see a picture of small-scale, rapid mass input from spicules -- those spicules also trace out the motion of the waves (like seaweed waving at the bottom of the ocean). We are learning that there are a minimum of two things going on that can drive material and energy upward. The next puzzle is to model them and figure out how they work together to produce what we observe.

Can you describe the technology that helped in this study?
SDO is a pretty advanced telescope with a huge data load per day of close to 2Tb. It takes images of the sun in 10 wavelengths of light in 16 megapixel images every 12s. The very clean, well designed optics of the telescope allow us to see the motion of very faint structures. It will change the way we see and understand the Sun. Unlike TRACE, which was kind of like a prototype, it covers the whole Sun, and so we can see just how connected events are in a global way -- by taking images every 12s we can see that global eruptions can be intimately connected with one another.

What previous research are these new observations built off of?
Basically three papers:

1. Tomczyk et al. 2007, Science, 317, 1192
*identified Alfvenic waves in the Doppler movies of the corona, but they appeared to not have that much energy. No intensity, line width, polarization variations were observed to be associated with the waves

2. De Pontieu et al. 2007, Science, 318, 1574
*discovered thermite whole limb of the sun underwent rigorous Alfvenic motion. The spicules allowed us to trace put the motion and see how much energy was in the chompspheric waves

3. De Pontieu et al. 2011, Science, 331, 55
*identified the plasma connection between the chompspheric jets and the injection of coronal mass

How can your results be applied to understanding how the waves lose their energy?
We have established a lot of the observed properties of the waves, then the modelers can use those values in their models to see what happens.....we wait!

________________________________

April Garbuz is a TalkingScience summer intern and a junior at Wilton High School. She loves science, debating, acting, and swimming. Ultimately, she'd like to be a research scientist.

 

About April Garbuz

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