lunes, 2 de agosto de 2010
"Spacequakes" Discovered in Earth's Upper Atmosphere
The sun can dump enough energy into Earth's magnetic field to trigger "spacequakes" in our planet's upper atmosphere, a new study has found.
The space weather phenomenon—technically a strong vibration in the planet's magnetic field—can affect auroras and can spawn "space twisters" capable of bringing down power lines.
In general, Earth's magnetic field lines can be thought of as rubber bands stretched taut by the solar wind, which is actually charged particles flowing in all directions from the sun, said study co-author Vassilis Angelopoulos, a space physicist at the University of California, Los Angeles.
Earth's magnetic tail is the part of the field that's stretched out like a windsock by the sun's steady bombardment.
New data from a suite of NASA satellites called THEMIS (Time History of Events and Macroscale Interactions during Substorms) show that, when a magnetic field line in the tail builds up too much energy, it snaps, and part of the line is sent hurtling back toward Earth.
In the process, the broken line can attract high-energy particles in Earth's atmosphere to create a whip-like "plasma jet."
These jets crash into other parts of Earth's magnetic field at about 20,000 miles (32,000 kilometers) above the planet's surface, where they bounce like tennis balls hitting a carpet.
"We have learned that the plasma jets from the magnetic tail bounce and then bounce again, and so on, till they eventually lose all their energy," said Angelopoulos, also the principal investigator for THEMIS.
Each set of plasma jet impacts can release as much energy in total as a magnitude 5 to 6 earthquake, THEMIS revealed.
Spacequakes Spawn Magnetic Twisters
In addition, the impacts set Earth's entire magnetic field vibrating, and they create highly magnetic vortices, or space twisters, that penetrate down into the planet's atmosphere.
These vortices twirl Earth's magnetic field lines in the North and South Poles, where they can create bright ripples and whirls in auroras.
The effects of the vortices can even be felt on the ground, as they can induce current spikes in electrical lines that can bring down power grids over large areas.
By watching for spacequakes at polar monitoring stations—or even by looking at the visible effects in auroras—scientists can tell that major spacequakes happen about once a year, Angelopoulos said.
Smaller ones happen about once every four hours, he added, so "we have plenty of opportunities to study them."
The spacequakes study appears in the April issue of the journal Geophysical Research Letters.