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Thursday, August 23, 2007

The Sun and I

As most of you know, I have ventured into the realm of solar modeling in my research here at Colorado. Specifically, I work of global-scale models of the sun's convection zone, which extends from about 75% of the sun's radius to about 98% of the sun's radius. In this area, energy is being transported mainly by convection - hot fluid rises and cold fluid sinks. When you add a magnetic field, this creates a self-sustaining dynamo that turns convective energy into magnetic energy, which creates a sustained magnetic field in the sun's convection zone.

Magnetic fields play an important role in solar activity. When magnetic field lines poke up out of the solar surface, you get sun spots, flares, and coronal mass ejections - the fireworks. In order to better understand what is driving these explosive events, we need to better understand what is driving the sun's magnetic field and how it changes in time.

Below is a movie created from data from our numerical models of the sun's convection zone. This particular model has been "spun-up" to three times the solar rotation rate in order to exaggerate the effects and speed up the solar cycles. A normal solar magnetic cycle takes 22 years - in this simulation, we see strong magnetic variability in cycles that take about 2 years of simulation time. The movie specifically shows some 3-D visualizations of the toroidal magnetic field (i.e. the magnetic field with the dipole part removed). The positive (in the direction of the sun's rotation) field is displayed in red (strongest) to yellow (weakest). The negative field is displayed in blue (strongest) to purple (weakest). For ease of viewing, only the strong fields are displayed.
video
As you can see, the magnetic field has organized itself into two bands of magnetic field in the tropics. In this cycle, both bands have been greatly weakened in the second image - particularly the negative (blue/purple) band. Since our model uses constant inner and outer boundary conditions, this clearly shows that the sun's magnetic variability can be caused purely by oscillations in the convection zone.

Aside from the science we are able to do with these types of visualizations, it's also just fun to be able to actually see the 3-D data we work with. In the future, I think that 3-D visualizations are going to become more and more common as more numerical models progress into three dimensions.

These videos were created using Vista, developed at the San Diego Supercomputing Center. Special thanks to Steve Cutchin at SDSC for working with me to get Vista running with our data.

2 comments:

  1. Those are neat videos. I'm glad you got the wide screen to work. So, above 98% of the radius, between 98-100%, does the convection behave differently?

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  2. The top two percent of the sun is the photosphere and there you start to super-sonic flows and shock waves, which our code doesn't handle well. We are working on an extension of our code that will hopefully get us out to 99.5% of the solar radius soon, but for now, 98% is as far as we go.

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