Cracking the Mysteries of Space Weather
02.09.12
Our planet is mostly protected from solar flares, coronal mass ejections, and other space weather events by a cocoon of magnetic field called the magnetosphere.
March 1989: A power blackout in Canada affects 6 million people.
October-November 2003: Solar panels fail on the $450 million Midori 2 research satellite, and astronauts take cover in the International Space Station.
June 2011: Airlines report disruption of high-frequency radio communications near the Arctic.
These incidents all resulted from space weather—giant storms of plasma (ionized gas) and magnetic fields propelled from the sun along the solar wind.
Our planet is mostly protected from solar flares, coronal mass ejections, and other space weather events by a cocoon of magnetic field called the magnetosphere. But sometimes Earth's magnetosphere "cracks" and lets space weather inside, where it can cause damage. Satellites losses alone exceed $4 billion.
Observations and simulations show that "magnetic reconnection is the predominant mechanism that fractures Earth's protective magnetic shield," said Homa Karimabadi, space physics group leader at the University of California, San Diego and chief scientist at SciberQuest, Inc. In magnetic reconnection, magnetic field lines explosively break apart and connect with other field lines to form new configurations. "If it weren't for reconnection, Earth's magnetic field would be able to deflect nearly everything coming from the Sun," he said.
Using NASA's Pleiades supercomputer and other resources, Karimabadi's group is running petascale simulations to better understand magnetic reconnection and how it can crack the magnetosphere.
Local to Global Simulations
Getting the details of space weather right means capturing everything from the 1.28 million-kilometer-sized magnetosphere down to subatomic-scale electrons. Doing that in one simulation would require supercomputers more than 1,000 times faster than those available today, so the research team breaks the problem into two parts.
They start with "local" simulations that include full electron physics of regions in the magnetosphere where reconnection is known to occur. "We study the efficiency of reconnection under different conditions in the magnetosphere. This includes such things as the amount of mixing of the plasma from the solar wind and from the magnetosphere," Karimabadi said. The team then uses the local-scale details to improve models of magnetic reconnection in "global" simulations encompassing a region starting at about 3 earth radii (1 earth radius is about 6,400 kilometers) and extending to 30–200 radii.
Accessing up to 25,000 processor-cores on Pleiades, Karimabadi said his group can run "kinetic" simulations that treat each electron with its full properties and understand how electrons allow reconnection to occur. In the local simulations, electrons are treated as individual particles. In the global simulations, electrons are treated as fluids and ions (electrically charged atoms) as particles. With Pleiades' long queues, simulations can run for 5 days straight, enabling many parameter studies.
Turbulent Reconnection
Among recent findings is that magnetic reconnection by itself is quite turbulent, producing vortices in the plasma that create many interacting flux ropes—twisted bundles of magnetic field. As observed by spacecraft, flux ropes can extend several times the radius of Earth.
"Our simulations show that the flux ropes start at electron scales and grow to very large scales," Karimabadi said. The flux rope interactions lead to turbulent mixing of magnetic field and plasma. This enhanced mixing lets the solar wind enter different regions of the magnetosphere more effectively.
Such model predictions compare well with observations from satellites including Cluster and THEMIS. Karimabadi's team also is helping NASA plan the Magnetospheric Multiscale (MMS) mission scheduled to launch in 2014. MMS will focus on studying magnetic reconnection at resolutions approaching 10 kilometers.
"Incorporating parameters from the latest observations, our approach is to better understand the physics and update the kinetic models," Karimabadi said. "Capturing more of the physics will eventually allow us to develop more accurate forecast models."
Jarrett Cohen, NASA Goddard Space Flight Center
Karimabadi's research team includes:
William Daughton; Los Alamos National Laboratory
Burlen Loring; Lawrence Berkeley National Laboratory
Amit Majumdar; SDSC
Yuri Omelchenko; UCSD
Vadim Roytershteyn; UCSD
Tamara Sipes; SDSC
Mahidhar Tatineni; SDSC
Hoanh Vu; UCSD
Related Links
Contact Information:
Homa Karimabadi
Space Physics Group Leader/Chief Scientist
University of California, San Diego/SciberQuest, Inc.
homa@ece.ucsd.edu
(858) 793-7063
