4 posts tagged “the sun”
David Bebee/Waterloo Region Record, via Associated Press
A NASA mission to study geomagnetic storms used satellites and ground observations to determine the order of events surrounding the aurora borealis, shown in Kitchener, Ontario, in 2004.
By KENNETH CHANG
The New York Times
Published: July 25, 2008
Scientists say they have discovered what makes the northern lights dance.
Researchers working on a NASA mission to understand the interplay of magnetic fields and charged particles blown outward from the Sun have identified the trigger for the colorful electrical storms in the polar regions. They hope this is a step in developing reliable forecasts of geomagnetic storms that can disrupt satellites in orbit and power grids on the ground.
The findings appeared in an article published Thursday on the Web site of the journal Science.
Scientists have long known that the dancing auroras of color known as the northern and southern lights are generated by charged particles flying from the Sun and interacting with the Earth’s magnetic field, which is then pulled into a windsock shape by the solar wind.
Turbulent storms on the Sun generate extremely bright auroral displays, but even in quieter times, smaller events known as substorms still generate the lights.
“They happen every three or four hours,” said Vassilis Angelopoulos, a professor of earth and space sciences at University of California, Los Angeles, and principal investigator of a NASA mission called Themis, short for Time, History of Events and Macroscale Interactions during Substorms. “The Earth’s environment stores energy. Then all of a sudden it releases it.”
Each substorm generates a current of about one million to two million amps over one to two hours, or a total energy equivalent to a magnitude-5 or magnitude-6 earthquake, Dr. Angelopoulos said.
Scientists knew two events that occur in the tail of the magnetic field during substorms, but did not know which event acted as the trigger for the auroras.
Over the past 30 years, some scientists have believed that a disruption in the current of charged particles — similar to the blowing of an electric fuse, the scientists said — about one-sixth of the distance from the Earth to the Moon’s orbit was responsible. Others believed it was a snapping of magnetic field lines farther out, about one-third of the distance to the Moon.
To answer the question, the Themis mission launched five identical satellites, each about the size of a washing machine, to measure the electric and magnetic fields as well as the particles passing by at different locations around Earth. Coupled with ground observations, scientists were able to deduce the order of events in a substorm in February.
The snapping of magnetic fields occurred first, followed by a burst of auroras. Surprisingly, the disruption in the charged particle current occurred after the aurora. Proponents of that hypothesis had thought that the magnetic snapping caused the change in electric current and that, in turn, led to the auroras.
“This defies our old paradigms,” Dr. Angelopoulos said.
Next, Dr. Angelopoulos said, scientists will try to figure out exactly why the magnetic field lines snap. With a better understanding of substorms, scientists would like to understand what happens during the larger storms. They hope to have better prediction methods working by the time the next peak of solar storms arrives between 2010 and 2012.
What's Wrong with the Sun? (Nothing) |
07.11.2008
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+ Play Audio | + Download Audio | + Email to a friend | + Join mailing list July 11, 2008: Stop the presses! The sun is behaving normally. So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle." This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise. But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."
Above: The solar cycle, 1995-2015. The "noisy" curve traces measured sunspot numbers; the smoothed curves are predictions. Credit: D. Hathaway/NASA/MSFC. [more] During Solar Max, huge sunspots and intense solar flares are a daily occurance. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001. During Solar Minimum, the opposite occurs. Solar flares are almost non-existant while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.
"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then. Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values." In summary, "the current minimum is not abnormally low or long." The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.
For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again. The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally." What's next? Hathaway anticipates more spotless days1, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012. Stay tuned to Science@NASA for updates. Author: Dr. Tony Phillips | Credit: Science@NASA
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13 May 2008
Is something lurking just over the sun's eastern limb? Yesterday's impressive display suggests the answer is yes. Amateur astronomers in Europe and North America witnessed fountains of hot, magnetized gas surging over the eastern edge of the sun. "My hard drive is full of movies," says Didier Favre of Brétigny sur Orge, France, who counted no fewer than seven eruptions.
Veteran observer Pete Lawrence of Selsey, UK, took the picture above. "This is the first time I've ever seen material moving visually away from the surface of the Sun," he says. "What a treat!"
Readers, if you have a solar telescope, train it on the eastern edge of the sun. "The area," says Lawrence, "appears full of promise."
UPDATE: Observers are reporting a sunspot (or proto-sunspot) emerging from the direction of yesterday's prominence: #1, #2, #3.
more images: from Britta Suhre of Dortmund, Germany; from Monty Leventhal of Sydney, Australia; from Les Cowley of eastern England; from Stephen Ames of Hodgenville, Kentucky; from Cai-Uso Wohler of Bispingen, Germany; from C. Miller and J. Stetson of South Portland, Maine; from Malcolm Park of London, England.SOLAR BLAST: No sunspots? No problem. Yesterday the blank sun unleashed a solar flare without the usual aid of a sunspot. At 1408 UT on April 26th, Earth-orbiting satellites detected a surge of X-rays registering B3.8 on the Richter scale of solar flares. Shortly thereafter, SOHO coronagraphs photographed a coronal mass ejection (CME) billowing away from the sun:
The expanding cloud could deliver a glancing blow to Earth's magnetic field late on April 28th or 29th. High-latitude sky watchers should be alert for auroras when it arrives.
This strange solar flare came from a patch of sun (N08,E08) where magnetic fields were not intense enough to form a visible sunspot (sunspots are made of magnetism). Nevertheless, magnetic fields were present with sufficient energy and instability to produce a powerful explosion. NASA's twin STEREO spacecraft, observing the sun from widely separated vantage points, recorded a million mph shock wave or "solar tsunami" spreading from the blast site through the sun's atmosphere: movie.
Not bad for a "blank sun." Stay tuned for updates.
more images: from David Strange of Branscombe, Devon, UK; from Emiel Veldhuis of Zwolle, the Netherlands; from Stephen Ames of Hodegenville, KY; from Will Gater of Bristol, UK; from Patricia Cannaerts of Belgium; from Joel Bavais of Anvaing, Belgium
