Showing posts with label SDO. Show all posts
Showing posts with label SDO. Show all posts

Thursday, February 11, 2010

Solar Dynamics Observatory




This is truly an exciting leap forward in mapping the underlying structures of the sun.

I note that the Maunder minimum gets the usual mention.  It seems that everyone insists on forgetting that our observations then were during the dawn of optical astronomy and it took a long time for observation protocols to be set up.  We have no reason to trust the data and less reason to consider earlier data which mostly does not exist.

By the time we got truly curious about sunspots we were past the Maunder minimum.  Thus I suspect that the lack of data may well not be evidence of a lack of phenomena.

Today we are sending out hardware able to collect data over a wide range of wavelengths and include methods for deep imaging of the solar dynamo itself.  This is bound to produce exciting new images that I look forward to seeing.

The real laugh on us though is to understand that the sun is a variable star in a radiation band we simply cannot see

Solar Dynamics Observatory: The 'Variable Sun' Mission

February 5, 2010: For some years now, an unorthodox idea has been gaining favor among astronomers. It contradicts old teachings and unsettles thoughtful observers, especially climatologists.


"The sun," explains Lika Guhathakurta of NASA headquarters in Washington DC, "is a variable star."

But it looks so constant...

That's only a limitation of the human eye. Modern telescopes and spacecraft have penetrated the sun's blinding glare and found a maelstrom of unpredictable turmoil. Solar flares explode with the power of a billion atomic bombs. Clouds of magnetized gas (CMEs) big enough to swallow planets break away from the stellar surface. Holes in the sun's atmosphere spew million mile-per-hour gusts of solar wind.
And those are the things that can happen in just one day.

Over longer periods of decades to centuries, solar activity waxes and wanes with a complex rhythm that researchers are still sorting out. The most famous "beat" is the 11-year sunspot cycle, described in many texts as a regular, clockwork process. In fact, it seems to have a mind of its own.

 "It's not even 11 years," says Guhathakurtha. "The cycle ranges in length from 9 to 12 years. Some cycles are intense, with many sunspots and solar flares; others are mild, with relatively little solar activity. In the 17th century, during a period called the 'Maunder Minimum,' the cycle appeared to stop altogether for about 70 years and no one knows why."

There is no need to go so far back in time, however, to find an example of the cycle's unpredictability. Right now the sun is climbing out of a century-class solar minimum that almost no one anticipated.

"The depth of the solar minimum in 2008-2009 really took us by surprise," says sunspot expert David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama. "It highlights how far we still have to go to successfully forecast solar activity."

That's a problem, because human society is increasingly vulnerable to solar flare ups. Modern people depend on a network of interconnected high-tech systems for the basics of daily life. Smart power grids, GPS navigation, air travel, financial services, emergency radio communications—they can all be knocked out by intense solar activity. According to a 2008 study by the National Academy of Sciences, a century-class solar storm could cause twenty times more economic damage than Hurricane Katrina.



http://science.nasa.gov/headlines/y2010/images/sdo/collapse_strip2.jpg

Right: Areas of the USA vulnerable to power system collapse in response to an extreme geomagnetic storm. Source: National Academy of Sciences. [more]

"Understanding solar variability is crucial," says space scientist Judith Lean of the Naval Research Lab in Washington DC. "Our modern way of life depends upon it."

Enter the Solar Dynamics Observatory—"SDO" for short—slated to launch on Feb. 9, 2010, from the Kennedy Space Center in Florida.

SDO is designed to probe solar variability unlike any other mission in NASA history. It will observe the sun faster, deeper, and in greater detail than previous observatories, breaking barriers of time-scale and clarity that have long blocked progress in solar physics.

Guhathakurta believes that "SDO is going to revolutionize our view of the sun."

The revolution begins with high-speed photography. SDO will record IMAX-quality images of the sun every 10 seconds using a bank of multi-wavelength telescopes called the Atmospheric Imaging Assembly (AIA). For comparison, previous observatories have taken pictures at best every few minutes with resolutions akin to what you see on the web, not at a movie theatre. Researchers believe that SDO's rapid-fire cadence could have the same transformative effect on solar physics that the invention of high-speed photography had on many sciences in the 19th century.

SDO doesn't stop at the stellar surface. SDO's Helioseismic Magnetic Imager (HMI) can actually look inside the sun at the solar dynamo itself.

The solar dynamo is a network of deep plasma currents that generates the sun's tangled and sometimes explosive magnetic field. It regulates all forms of solar activity from the lightning-fast eruptions of solar flares to the slow decadal undulations of the sunspot cycle.

"Understanding the inner workings of the solar dynamo has long been a 'holy grail' of solar physics," says Dean Pesnell of the Goddard Space Flight Center in Greenbelt, Maryland. "HMI could finally deliver this to us."

The dynamo is hidden from view by about 140,000 miles of overlying hot gas. SDO penetrates the veil using a technique familiar to geologists—seismology. Just as geologists probe Earth's interior using waves generated by earthquakes, solar physicists can probe the sun's interior using acoustic waves generated by the sun's own boiling turbulence. HMI detects the waves, which researchers on Earth can transform into fairly clear pictures.

"It's a little like taking an ultrasound of a pregnant mother," Pesnell explains. "We can see 'the baby' right through the skin."
______________________________________

Sidebar: 'Solar Constant' is an Oxymoron

Astronomers were once so convinced of the sun's constancy, they called the irradiance of the sun "the solar constant," and they set out to measure it as they would any constant of Nature. By definition, the solar constant is the amount of solar energy deposited at the top of Earth's atmosphere in units of watts per meter-squared. All wavelengths of radiation are included—radio, infrared, visible light, ultraviolet, x-rays and so on. The approximate value of the solar constant is 1361 W/m2.

Clouds, atmospheric absorption and other factors complicate measurements from Earth's surface, so NASA has taken the measuring devices to space. Today, VIRGO, ACRIM and SORCE are making measurements with precisions approaching 10 parts per million per year. Future instruments scheduled for flight on NASA's Glory and NOAA's NPOESS spacecraft aim for even higher precisions.
To the amazement of many researchers, the solar constant has turned out to be not constant.

"'Solar constant' is an oxymoron," says Judith Lean of the Naval Research Lab. "Satellite data show that the sun's total irradiance rises and falls with the sunspot cycle by a significant amount."



http://science.nasa.gov/headlines/y2010/images/sdo/sorcetim.jpg

Right: Measurements from the SORCE mission indicate that the variability of total solar irradiance has decreased over the past six years. [larger image] [movie]

At solar maximum, the sun is about 0.1% brighter than it is at solar minimum. That may not sound like much, but consider the following: A 0.1% change in 1361 W/m2 equals 1.4 Watts/m2. Averaging this number over the spherical Earth and correcting for Earth's reflectivity yields 0.24 Watts for every square meter of our planet.
_____________________________________

"Add it all up and you get a lot of energy," says Lean. "How this might affect weather and climate is a matter of—at times passionate—debate."

Because SDO specializes in extreme ultraviolet wavelengths, it won't be making direct measurements of the total solar irradiance, which requires sensitivity across the entire electromagnetic spectrum. Nevertheless, a combination of data from SDO and other spacecraft could shed new light on this important topic—and perhaps reveal other oxymorons as well.

Finally – and of most immediate relevance for Earth--SDO will observe the sun at wavelengths where the sun is most variable, the extreme ultraviolet (EUV). EUV photons are high-energy cousins of regular UV rays that cause sunburns. Fortunately, our atmosphere blocks solar EUV; otherwise a day at the beach could be fatal. In space, solar EUV emission is easy to detect and arguably the most sensitive indicator of solar activity.

"If human eyes could see EUV wavelengths, no one would doubt that the sun is a variable star," says Tom Woods of the University of Colorado in Boulder.

During a solar flare, the sun's extreme ultraviolet output can vary by factors of hundreds to thousands in a matter of seconds. Surges of EUV photons heat Earth's upper atmosphere, causing the atmosphere to "puff up" and drag down low-orbiting satellites. EUV rays also break apart atoms and molecules, creating a layer of ions in the upper atmosphere that can severely disturb radio signals. According to Judith Lean, "EUV controls Earth's environment throughout the entire atmosphere above about 100 km."

"EUV is where the action is," agrees Woods.

That's why Woods and colleagues built an extreme ultraviolet sensor for SDO called the EUV Variability Experiment ("EVE"). "EVE gives us the highest time resolution (10 sec) and the highest spectral resolution (< 0.1 nm) that we've ever had for measuring the sun, and we'll have it 24/7," he says. "This is a huge improvement over past missions."

Woods expects EVE to reveal how fast the sun can change—"we really don't know," he points out—and to surprise astronomers with the size of the outbursts.

EVE, AIA, HMI. For the next five years, the Solar Dynamics Observatory will use these instruments to redefine our star and its potential for variability. What unorthodox ideas will they beam back? Old teachings beware!

Thursday, June 18, 2009

Mystery of Missing Sun Spots

That they can track such jet streams is a revelation to outsiders. That it is behaving oddly is nicely associated with the low number of sunspots. So far it is tracking beautifully. We just want it to liven up at the same time as the sunspot count climbs.

Anyway, this paints a very natural process that acts like it has been doing this forever. And somehow we are developing a good working model of magnetic dynamics here. I like it.


Mystery of the Missing Sunspots, Solved?

06.17.2009 June 17, 2009: The sun is in the pits of a century-class solar minimum, and sunspots have been puzzlingly scarce for more than two years. Now, for the first time, solar physicists might understand why.

At an American Astronomical Society press conference today in Boulder, Colorado, researchers announced that a jet stream deep inside the sun is migrating slower than usual through the star's interior, giving rise to the current lack of sunspots.

Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.

http://science.nasa.gov/headlines/y2009/images/jetstream/sonogram.jpg


Above: A helioseismic map of the solar interior. Tilted red-yellow bands trace solar jet streams. Black contours denote sunspot activity. When the jet streams reach a critical latitude around 22 degrees, sunspot activity intensifies.

Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle.

The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead.

"It is exciting to see", says Hill, "that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging."

The current solar minimum has been so long and deep, it prompted some scientists to speculate that the sun might enter a long period with no sunspot activity at all, akin to the Maunder Minimum of the 17th century. This new result dispells those concerns. The sun's internal magnetic dynamo is still operating, and the sunspot cycle is not "broken."

Because it flows beneath the surface of the sun, the jet stream is not directly visible. Hill and Howe tracked its hidden motions via helioseismology. Shifting masses inside the sun send pressure waves rippling through the stellar interior. So-called "p modes" (p for pressure) bounce around the interior and cause the sun to ring like an enormous bell. By studying the vibrations of the sun's surface, it is possible to figure out what is happening inside. Similar techniques are used by geologists to map the interior of our planet.

In this case, researchers combined data from GONG and SOHO. GONG, short for "Global Oscillation Network Group," is an NSO-led network of telescopes that measures solar vibrations from various locations around Earth. SOHO, the Solar and Heliospheric Observatory, makes similar measurements from Earth orbit."This is an important discovery," says Dean Pesnell of NASA's Goddard Space Flight Center. "It shows how flows inside the sun are tied to the creation of sunspots and how jet streams can affect the timing of the solar cycle."

There is, however, much more to learn.

"We still don't understand exactly how jet streams trigger sunspot production," says Pesnell. "Nor do we fully understand how the jet streams themselves are generated."

To solve these mysteries, and others, NASA plans to launch the Solar Dynamics Observatory (SDO) later this year. SDO is equipped with sophisticated helioseismology sensors that will allow it to probe the solar interior better than ever before.

"The Helioseismic and Magnetic Imager (HMI) on SDO will improve our understanding of these jet streams and other internal flows by providing full disk images at ever-increasing depths in the sun," says Pesnell.

Continued tracking and study of solar jet streams could help researchers do something unprecedented--accurately predict the unfolding of future solar cycles. Stay tuned for that!