BY John Borland / December 12, 2007
“This system began observing an enormous substorm, or Northern Light event, on March 23, which helped trigger the discoveries. The storm moved faster than anyone had expected, crossing 15 degrees of longitude in a single minute, about 400 miles per hour. The entire two-hour event released about five hundred thousand billion Joules, or about as much energy as a magnitude 5.5 earthquake, researchers said. Over the next few months, the spacecraft encountered what researchers call magnetic ropes, essentially bundles of magnetic fields that are twisted together like twine. The first to be mapped by the THEMIS satellites was located about 40,000 miles above the Earth’s surface, in the magnetopause, and about as wide as the Earth itself. The magnetopause is the region where the solar wind – electrically charged particles that flow away from the sun at incredible speeds – crashes into the Earth’s magnetic field. The “rope” formed there and unraveled again over the course of just a few minutes, but in the process proved to be a significant conduit for solar wind energy. “The satellites have found evidence of magnetic ropes connecting Earth’s upper atmosphere directly to the sun,” said David Sibeck, project scientist for the mission at NASA’s Goddard Space Flight Center. “We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras.” The scientists have also observed the equivalent of a “bow shock,” as at the leading edge of a boat, where the front edge of Earth’s magnetic field first encounters the solar wind. Occasionally a burst of electrical current in the solar wind will hit this “bow shock,” creating an explosion, researchers said.”
MAGNETIC ROPES, TIED TO THE SUN
Space scientists at UCLA solve the mystery behind aurora borealis
BY Stuart Wolpert / 7/24/2008
UCLA space scientists and colleagues have identified the mechanism that triggers substorms in space; wreaks havoc on satellites, power grids and communications systems; and leads to the explosive release of energy that causes the spectacular brightening of the aurora borealis, also known as the northern lights. For 30 years, there have been two competing theories to explain the onset of these substorms, which are energy releases in the Earth’s magnetosphere, said Vassilis
Angelopoulos, a UCLA professor of Earth and space sciences and principal investigator of the NASA-funded mission known as THEMIS (Time History of Events and Macroscale Interactions during Substorms).
One theory is that the trigger happens relatively close to Earth, about one-sixth of the distance to the moon. According to this theory, large currents building up in the space environment, which is composed of charged ions and electrons, or “plasma,” are suddenly released by an explosive instability. The plasma implodes toward Earth as the space currents are disrupted, which is the start of the substorm. A second theory says the trigger is farther out, about one-third of the distance to the moon, and involves a different process: When two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.
Which theory is right?
“Our data show clearly and for the first time that magnetic reconnection is the trigger,” said Angelopoulos, who reports the research in the July 24 online issue of the journal Science. “Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening.” Previous studies of the Earth’s magnetosphere and space weather have been unable to pinpoint the origin of substorms, which are large magnetic disturbances. Ionized gas emitted from the sun’s surface speeds up as it moves away from the sun, attaining speeds of 1 million mph and interacting with the Earth’s upper atmosphere, which is also
ionized, Angelopoulos said. Substorms are building blocks of larger storms. “We need to understand this environment and eventually be able to predict when these large energy releases will happen so astronauts can go inside their spacecraft and we can turn off critical systems on satellites so they will not be damaged,” Angelopoulos said. “This has been exceedingly difficult in the past, because previous missions, which measured the plasma at one location, were unable to determine the origin of the large space storms. To resolve this question properly requires correlations and signal-timing at multiple locations. This is precisely what was missing until now.”
At high northern latitudes in the northern U.S. and Canada, shimmering bands of light called the aurora borealis, or northern lights, stretch across the sky from the east to the west. During the geomagnetically disturbed periods known as substorms, these bands of light brighten. These multicolored light shows are generated when showers of high-speed electrons descend along magnetic field lines to strike the Earth’s upper atmosphere. Scientists want to learn when, where and why solar wind energy stored within the Earth’s magnetosphere is explosively released to accelerate these electrons. THEMIS is establishing for the first time when and where substorms begin, determining how the individual components of substorms interact, and discovering how substorms power the aurora borealis. “We discovered what sparks the magnificent light show of the aurora,” Angelopoulos said.
THEMIS has five satellites — with electric, magnetic, ion and electron detectors — in carefully chosen orbits around the Earth and an array of 20 ground observatories with automated, all-sky cameras located in the northern U.S. and Canada that catch substorms as they happen. The ground observatories take images of the aurora in white light. One satellite is a third of the distance to the moon, one is about a fourth of the distance and three are about a sixth of the distance. The outermost satellite takes four days to orbit the Earth, the next one two days, and the closest ones orbit the Earth in just one day. Every four days, the satellites line up. As the satellites are measuring the magnetic and electric fields of the plasma above the Earth’s atmosphere once every four days, the ground-based observatories are imaging the auroral lights and the electrical currents from space that generate them. THEMIS was launched on Feb. 17, 2007, from Cape Canaveral, Fla., and is expected to observe approximately 30 substorms in its nominal lifetime. “Armed with this knowledge, we are not only putting to rest age-old questions about the origin of the spectacular auroral eruptions but will also be able to provide statistics on substorm evolution and model its effects on space weather,” Angelopoulos said.
The project received a NASA outstanding performance group award this May. THEMIS is managed by the Explorers Program Office at Goddard Space Flight Center in Maryland. THEMIS mission co-investigators include Christopher T. Russell, UCLA professor of geophysics and space physics and a co-author on the Science paper; Margaret G. Kivelson, professor of space physics in the UCLA Department of Earth and Space Sciences; Krishan Khurana, a researcher in the UCLA Department of
Earth and Space Sciences; and scientists from UC Berkeley, where the mission was put together and half the instruments were built, Germany, Austria, France, Russia, Japan, Canada and the U.S. Themis was the blindfolded Greek goddess of order and justice. In 1619 A.D., Galileo Galilei coined the term “aurora borealis” after Aurora, the Roman goddess of morning. He had the misconception that the auroras he saw were due to sunlight reflecting from the atmosphere.
email : vassilis [at] igpp.ucla [dot] edu / vassilis [at] ucla [dot] edu
Published Online July 24, 2008 / Science DOI: 10.1126/science.
Tail Reconnection Triggering Substorm Onset
Magnetospheric substorms explosively release solar wind energy previously stored in Earth’s magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at ~10 RE (RE = Earth Radius, or 6374 km), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at ~20 to 30 RE. We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 RE, at least 1.5 min before auroral intensification, at least 2 min before near-Earth current disruption, and about 3 min before substorm expansion. These results demonstrate that substorms are likely initiated by tail reconnection.
Vassilis Angelopoulos 1*, James P. McFadden 2, Davin Larson 2, Charles W. Carlson 2, Stephen B. Mende 2, Harald Frey 2, Tai Phan 2, David G. Sibeck 3, Karl-Heinz Glassmeier 4, Uli Auster 4, Eric Donovan 5, Ian R. Mann 6, I. Jonathan Rae 6, Christopher T. Russell 1, Andrei Runov 1, Xu-Zhi Zhou 1, Larry Kepko 7
1 IGPP/ESS, UCLA, Los Angeles, CA, USA.
2 Space Sciences Laboratory, University of California at Berkeley, CA, USA.
3 Code 674, NASA/GSFC, Greenbelt, MD, USA.
4 TUBS, Braunschweig, D-38106, Germany.
5 Department of Physics and Astronomy, University of Calgary, Calgary, Canada.
6 Department of Physics, University of Alberta, Edmonton, Alberta, Canada.
7 Space Science Center, University of New Hampshire, Durham, NH, USA.
“On January 4, 2008, a reversed-polarity sunspot appeared—and this signals the start of Solar Cycle 24,” says David Hathaway of the Marshall Space Flight Center. Solar activity waxes and wanes in 11-
year cycles. Lately, we’ve been experiencing the low ebb, “very few flares, sunspots, or activity of any kind,” says Hathaway. “Solar minimum is upon us.” The previous solar cycle, Solar Cycle 23, peaked in 2000-2002 with many furious solar storms. That cycle decayed as usual to the present quiet leaving solar physicists little to do other than wonder, when would the next cycle begin? The answer is now. “New solar cycles always begin with a high-latitude, reversed polarity sunspot,” explains Hathaway. “Reversed polarity” means a sunspot with opposite magnetic polarity compared to sunspots from the previous solar cycle. “High-latitude” refers to the sun’s grid of latitude and longitude. Old cycle spots congregate near the sun’s equator. New cycle spots appear higher, around 25 or 30 degrees latitude.
The sunspot that appeared on January 4th fits both these criteria. It was high latitude (30 degrees N) and magnetically reversed. NOAA named the spot AR10981, or “sunspot 981” for short. Sunspot 981 was small– only about as wide as Earth, which counts as small on the grand scale of the sun–and it has already faded away. But its three day appearance on Jan. 4-6 was enough to convince most solar physicists that Solar Cycle 24 is underway. Doug Biesecker of NOAA’s Space Weather Prediction Center in Boulder, Colorado, likens sunspot 981 “to the first robin of spring. There’s still snow on the ground, but the seasons are changing.” Last year, Biesecker chaired the Solar Cycle 24 Prediction Panel, an international group of experts from many universities and government agencies. “We predicted that Solar Cycle 24 would begin around March 2008 and it looks like we weren’t far off,” he says.
The onset of a new solar cycle is significant because of our increasingly space-based technological society. “Solar storms can disable satellites that we depend on for weather forecasts and GPS
navigation,” says Hathaway. Radio bursts from solar flares can directly interfere with cell phone reception while coronal mass ejections (CMEs) hitting Earth can cause electrical power outages. “The most famous example is the Quebec outage of 1989, which left some Canadians without power for as much as six days.” Air travel can be affected, too. Every year, intercontinental flights
carry thousands of passengers over Earth’s poles. It’s the shortest distance between, say, New York and Tokyo or Beijing and Chicago. In 1999, United Airlines made just twelve trips over the Arctic. By 2005, the number of flights had ballooned to 1,402. Other airlines report similar growth. “Solar storms have a big effect on polar regions of our planet,” says Steve Hill of the Space Weather Prediction Center. “When airplanes fly over the poles during solar storms, they can experience radio blackouts, navigation errors and computer reboots all caused by space radiation.” Avoiding the poles during solar storms solves the problem, but it costs extra time, money and fuel to “take the long way around.”
Now for the good news: More solar storms also means more auroras—”the greatest show on Earth.” During the last solar maximum, Northern Lights were spotted as far south as Arizona, Florida and California. Not so long ago, only visitors to the Arctic regularly enjoyed auroras, but with increasing attention to space weather and constantly improving forecasts, millions of people at all latitudes will know when to go out and look. Much of this is still years away. “Intense solar activity won’t begin immediately,” notes Hathaway. “Solar cycles usually take a few years to build from solar minimum (where we are now) to Solar Max, expected in 2011 or 2012.”
AURORAS AS SEEN FROM THE INT’L SPACE STATION
FLY THE BOREALIS
Virgin Galactic to Offer Space Cruise through Aurora Borealis /
January 09, 2008
Imagine what kind of spectacular show it would be like to fly into the heart of the Northern Lights. You may not have to imagine forever. Richard Branson has been busy thinking up new ways to get people excited about private space tourism, and he’s come up with something pretty spectacular. He’s offering to fly the affluent into the world’s biggest lightshow, the Aurora Borealis. The New Mexico Virgin Galactic Spaceport isn’t scheduled for completion until 2010, but Branson is already planning his next project from an Arctic launchpad located in the far north of Sweden in the small town of Kiruna. The Arctic location provides the town with unrivalled views of the spectacular
The aurora borealis is named after the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas. It often appears as a greenish glow with hints of red and purple. The green and red emissions come from atomic oxygen. Molecular nitrogen and nitrogen ions produce some of the low level red and very high blue /violet aurorae. The lights most often occur from September to October and from March to April. The Auroras are produced by the collision of charged particles from the magnetosphere, with atoms and molecules of the Earth’s upper atmosphere. The particles originate from the sun and arrive at the vicinity of earth in the relatively low-energy solar wind. Magnetic reconnection accelerates the particles towards earth. Kiruna already has an existing base called Esrange. Launching humans into an active aurora is more for excitement than science, but it has been deemed to be safe. Dr Olle Norberg, Esrange’s director, said they’ve done the research. “Is there a build-up of charge on the spacecraft? What is the radiation dose that you would receive? Those studies came out saying it is safe to do this.” Safe, and undoubtedly an incredible view.
MAGNETOSPHERES AND YOU
GANYMEDE MAGNETOPSHERE AS SOUND FILE
“This Quicktime Movie (3.9MB) allows you to hear the plasma waves observed by the Galileo Plasma Wave Receiver as it flew past Ganymede. The image is a dynamic spectrogram showing the intensity of waves as a function of frequency (vertical axis) and time (horizontal axis) in which red indicates high intensity waves and blue indicates low intensities. This spectrogram was obtained by Fourier transforming the actual waveform from the electric antenna at a sample rate of 201,600 samples per second. We have used the same waveform to generate an audio signal but have used a sample rate of about a factor of 9 slower in order to shift the 80-kHz bandwidth down into the audio frequency range. We have also used a technique called time-slicing to reduce the 45-minute recording to just one minute. The cursor moves across the spectrogram as the audio signal is played.”
EARTH’S POLES TO FLIP
Earth’s poles long overdue for reversal
BY Claire Thomas / 5 May 2008
A reversal of the Earth’s magnetic poles could happen sooner than we think, according to Dutch scientists who report that the planet’s magnetic field is becoming gradually less stable. A reversal could affect everything from navigation and communications equipment to the composition of the atmosphere, say experts. The report, published today in the U.K. journal Nature Geoscience, found that reversals have been far more common in the last 200 million years than they were deep in the planet’s history. Researchers, led by Andrew Biggin of the University of Utrecht in the Netherlands, made the discovery by analysing rocks formed between 2.45 to 2.82 billion years ago. The story of the Earth’s magnetic field is written in rocks over time. Because these rocks become ‘magnetised’ at
the time of their formation, scientists can discover which direction the poles were facing and how strong the Earth’s magnetic field was at that time. The magnetic poles wander around the vicinity of the geographic poles all the time – the north magnetic pole currently resides in the Canadian Arctic. However, at relatively regular intervals throughout the 4.5 billion year history of the planet, the magnetic poles have flipped completely. A few thousand years before a reversal, the magnetic field gradually gets weaker; something which could cause problems for inhabitants of the planet. “The Earth’s magnetic field is important for shielding the atmosphere, and us, from damage caused by the solar wind,” explained Biggin. “It’s also used by us and other species for navigation”. An increase in solar wind would disrupt communications equipment and power grids.
Current records suggest that we are long overdue for our next reversal, he said. “On average, there is a reversal around every 400,000 years, but this varies a lot.” The geological record suggests that the last reversal was around 800,000 years ago. Furthermore, there is already evidence to show that the field has been weakening over the last few centuries – some archaeological remains suggest that the field was far stronger in the time of the Roman Empire, some 2,000 years ago. Don’t throw away your compass just yet though – major changes may not even happen in our lifetimes. “The reversal process is very unpredictable,” said Biggin. “We could be heading into a reversal in the next few centuries, or we might be waiting another million years”. Even then, reversal is a slow process, which can take some thousands of years to complete. But what about the effect on living organisms? Another paper, published in Nature in March suggested that some species that rely on the field for navigation or orientation have taken a knock from pole reversals in the past. Author David Gubbins, of the University of Leeds in England, said that some single-celled organisms that relied on magnetism to tell up from down likely went extinct during past reversals. Human beings have survived reversals in the past, however, added Gubbins, “so we are likely to come through the next one unscathed.”
email : biggin [at] geo [dot] uu [dot] nl
d.gubbins [at] see.leeds.ac [dot] uk
PREVIOUSLY ON SPECTRE — STARS HAVE WEATHER
SOLAR FLARES, AND OTHER PROTECTIONS
WHAT THE SUN SOUNDS LIKE
SPACE SMELLS LIKE
THE SMELL OF MOONDUST