Our Planet, Tangled in Magnetic Spaghetti


OK, so it’s not real spaghetti — it’s a computer visualization of the complex magnetic field that creates Earth’s magnetosphere — but it sure looks tangled.

Using the awesome power of a Cray XT5 Jaguar supercomputer, a team of space physicists are unlocking some of the biggest mysteries surrounding how the sun’s magnetic field interacts with our planet’s magnetosphere. They basically want to understand what happens when global magnetic fields become tangled to the extreme.

Space physicists categorize these interactions under “space weather,” and they are responsible for some of the Earth’s most powerful (and beautiful) atmospheric events.

“When a storm goes off on the sun, we can’t really predict the extent of damage that it will cause here on Earth. It is critical that we develop this predictive capability,” said Homa Karimabadi, a space physicist at the University of California-San Diego (UCSD).

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Computer simulations are a critical tool for space weather prediction, and with the help of one of the most powerful supercomputers in the world (that is capable of a peak performance of 2.33 petaFLOPS), the complex magnetohydrodynamics of a geomagnetic storm can be better understood.

It’s All In The Magnetic Fluid Motion

Put very simply, the tough physics behind “magnetohydrodynamics” can be split into three parts: magneto = magnetic, hydro = fluid, dynamics = motion. Each part represents complex calculations of how space plasma — from the hot, glowing, turbulent plasma on the solar surface, to the tenuous, wispy, high-energy ions that makes up the solar wind — acts.

So, should the sun unleash a coronal mass ejection (CME) in the direction of Earth (like it did at the end of last month), it would be useful to model the impact of this magnetic bubble of high-energy plasma before it hits our magnetosphere. Such an event involves a lot of magnetic-fluid-motion!

“With petascale computing we can now perform 3D global particle simulations of the magnetosphere that treat the ions as particles, but the electrons are kept as a fluid,” said Karimabadi. “It is now possible to address these problems at a resolution that was well out of reach until recently.”

With all this computing power, Karimabadi and his team have been able to simulate the phenomenon of “magnetic reconnection” — a phenomenon that can occur when two magnetic fields are forced together. The physics are hard to interpret, so the plasma needs to be simulated as a fluid and individual particles, all responding to the presence of a magnetic field.

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Should the conditions be “just right” during a solar storm, for example, the magnetic field of an incoming CME and the magnetosphere may be aligned — or “geo-effective” — so that the two fields snap and reconnect, creating an entry point for energetic solar particles to flood into the outer layers of the Earth’s magnetic field. Geomagnetic storms are often the result, generating stunning aurorae at high latitudes and powerful electrical currents through the atmosphere.

These electrical currents can cause problems on the ground, especially if we are caught unprepared. Predicting the occurrence of these currents are very useful to power companies, say. Should a “geo-effective” CME thump the magnetosphere, they’ll know a geomagnetic storm is coming and managers may decide to take measures to avoid power outages.

Key to understanding how the plasma and magnetic field from the sun interacts with our magnetosphere is to understand the amount of turbulence generated during a CME impact. “One of the surprising outcomes of our research is the ubiquity and nature of turbulence in the magnetosphere,” said Karimabadi. “This is important since turbulence implies more efficient mixing of the plasma and fields, and after all, space weather arises because the plasma and fields emanating from the sun can penetrate and mix with the plasma and fields of Earth’s magnetosphere.”

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And therein lies the power of the supercomputer and its ability to visualize dynamic 3D magnetic structures. “By color coding the magnetic field lines in our visualizations of the solar wind and the magnetosphere, we can track the level of (turbulent) mixing,” he added.

For more on this fascinating research, and to geek out on the awesomeness behind the Cray XT5 Jaguar supercomputer, read the Oak Ridge National Laboratory press release.

Image: Snapshot of the supercomputer simulation showing the tangled magnetic field of the Earth’s magnetosphere. Credit: OLCF

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