Saturday, June 30, 2012



Uploaded by  on Jul 29, 2010 Researchers using NASA's fleet of five THEMIS spacecraft have discovered a form of space weather that packs the punch of an earthquake and plays a key role in sparking bright Northern Lights. They call it "the spacequake." A spacequake is a temblor in Earth's magnetic field. It is felt most strongly in Earth orbit, but is not exclusive to space. The effects can reach all the way down to the surface of Earth itself.

"Magnetic reverberations have been detected at ground stations all around the globe, much like seismic detectors measure a large earthquake," says THEMIS principal investigator Vassilis Angelopoulos of UCLA.

It's an apt analogy because "the total energy in a spacequake can rival that of a magnitude 5 or 6 earthquake," according to Evgeny Panov of the Space Research Institute in Austria. Panov is first author of a paper reporting the results in the April 2010 issue of Geophysical Research Letters (GRL).

In 2007, THEMIS discovered the precursors of spacequakes. The action begins in Earth's magnetic tail, which is stretched out like a windsock by the million mph solar wind. Sometimes the tail can become so stretched and tension-filled, it snaps back like an over-torqued rubber band. Solar wind plasma trapped in the tail hurtles toward Earth. On more than one occasion, the five THEMIS spacecraft were in the line of fire when these "plasma jets" swept by. Clearly, the jets were going to hit Earth. But what would happen then? The fleet moved closer to the planet to find out.
"Now we know," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "Plasma jets trigger spacequakes."
According to THEMIS, the jets crash into the geomagnetic field some 30,000 km above Earth's equator. The impact sets off a rebounding process, in which the incoming plasma actually bounces up and down on the reverberating magnetic field. Researchers call it "repetitive flow rebuffing." It's akin to a tennis ball bouncing up and down on a carpeted floor. The first bounce is a big one, followed by bounces of decreasing amplitude as energy is dissipated in the carpet.

"We've long suspected that something like this was happening," says Sibeck. "By observing the process in situ, however, THEMIS has discovered something new and surprising."

The surprise is plasma vortices, huge whirls of magnetized gas as wide as Earth itself, spinning on the verge of the quaking magnetic field.

"When plasma jets hit the inner magnetosphere, vortices with opposite sense of rotation appear and reappear on either side of the plasma jet," explains Rumi Nakamura of the Space Research Institute in Austria, a co-author of the study. "We believe the vortices can generate substantial electrical currents in the near-Earth environment."

Acting together, vortices and spacequakes could have a noticeable effect on Earth. The tails of vortices may funnel particles into Earth's atmosphere, sparking auroras and making waves of ionization that disturb radio communications and GPS. By tugging on surface magnetic fields, spacequakes generate currents in the very ground we walk on. Ground current surges can have profound consequences, in extreme cases bringing down power grids over a wide area.

After THEMIS discovered the jets and quakes, Joachim Birn of the Los Alamos National Lab in New Mexico conducted a computer simulation of the rebounding process. Lo and behold, vortices appeared in good accord with THEMIS measurements. Moreover, the simulations suggest that the rebounding process can be seen from Earth's surface in the form of ripples and whirls in auroral displays. Ground stations report just such a phenomenon.

"It's a complicated process, but it all fits together," says Sibeck.

The work isn't finished. "We still have a lot to learn," he adds. "How big can spacequakes become? How many vortices can swirl around Earth at once--and how do they interact with one another?"

Image credit: CC 3.0 R N Marshman


Posted on Friday, 11 March, 2011 |  1 comment
Columnist: William B Stoecker

We live for the most part on the surface of the land, although we travel through the sky and on the surface of the sea. Rarely do most of us venture underground, and never to any great depth. Only two men have been to the deepest trench in the sea, and only a handful have ventured far beyond our atmosphere. And strange and sometimes frightening mysteries emerge from under the sea, under the Earth, and, especially, from the sky. It is in the sky (and sometimes emerging from or entering the sea) that we see UFOs. Blocks of ice, fish, frogs, and other things fall from the sky, with no explanation. And then there are the “skyquakes”…loud, booming sounds, rather like cannon fire, with no known origin.

The small town of Moodus, Connecticut is plagued by loud booms that seem to come from the area of Cave Hill and Mt. Tom. Skeptics attribute these noises to shallow earthquakes, and there was a real earthquake there on 5/6/1791, but no tremors have been recorded when the noises are heard. The local Algonquin and other Indians believed that the noises were caused by the demon Hobomock, and called the area “Matchimoodus” or”Matchemadoset,” meaning “place of bad noises.”

Barisal, on the Bay of Bengal in Bangladesh at the mouth of the Ganges River, has the “Barisal Guns.” Beginning at least as far back as the eighteen seventies, there were reports of “cannon fire” in groups of two or three, coming from the south or southwest (the Bay), usually from February through October, and seldom from November through January, with no earthquakes detected or thunderstorms reported. The monsoon usually arrives in June and lasts through September, covering only part of the time when the “guns” are commonly heard.

Similar mysterious booming sounds are called “mistpoeffers” in Belgium and the Netherlands, or “marinas” or “brontodi” in Italy, “retembos” in the Philippines, and “fog guns” in several other places. Loud booms have been reported from Western Australia and the State of Victoria, from New Brunswick, Canada near Passamquoddy Bay, Cedar Keys in Florida, Lough Neagh in Ireland, the Adriatic, northern Georgia (the one in the United States), and Franklinville, New York. In New York State they are called the “Seneca Guns.” Lewis and Clark reported a mysterious booming sound on 7/4/1805.


MASSIVE PROMINENCE: Amateur astronomers around the world are monitoring a massive, active prominence dancing along the sun's southeastern limb. If you have a solar telescope, take a look. The latest images suggest an eruption might be in the offing. Stay tuned for action.

DARK HOLE IN THE SUN'S ATMOSPHEREUltraviolet telescopes onboard NASA's Solar Dynamics Observatory are monitoring a vast dark hole--a "coronal hole"--in the sun's upper atmosphere. It has just turned directly toward Earth:
Coronal holes are places where the sun's magnetic field opens up and allows the solar wind to escape. A stream of solar wind flowing from this particular gap is en route to Earth, due to arrive on July 2nd or 3rd. The impact could spark geomagnetic storms and auroras. 

ACTIVE SUNSPOT: Sunspot AR1513 is crackling with impulsive M-class solar flares. NASA's Solar Dynamics Observatory recorded the extreme ultraviolet flash from one of them at 0920 UT on June 29th:
This M2-class flare illuminated Earth's upper atmosphere with a pulse of X-rays and extreme ultraviolet radiation. Waves of ionization rippled over Europe, altering the propagation of low-frequency radio signals around the continent. Using a receiver tuned to 60 kHz, Rob Stammes detected the sudden ionospheric disturbance over Norway. His antennas also picked up radio waves from the flare itself at 26 MHz and 56 MHz.
More ionization waves and solar radio bursts are in the offing. NOAA forecasters estimate a 40% chance of continued M-flares during the next 24 hours.

Solar wind
speed: 637.1 km/sec
density: 3.5 protons/cm3
explanation | more dataUpdated: Today at 2025 UT
X-ray Solar Flares
6-hr max: M1 
1832 UT Jun30 
24-hr: M1 
1832 UT Jun30 
explanation | more dataUpdated: Today at: 2000 UT

No comments: