Category: Solar Astronomy

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Seriously, I don’t think we should stare at this too long … but for scientists who plan to, this new, high-resolution view of a sunspot stands to unlock secrets of the Sun’s mysterious energetics.

In the just-released image above, the interface between a sunspot’s umbra (dark center) and penumbra (lighter outer region) shows a complex structure with narrow, almost horizontal (lighter to white) filaments embedded in a background having a more vertical (darker to black) magnetic field. Farther out, extended patches of horizontal field dominate. For the first time, scientists have modeled this complex structure in a comprehensive 3D computer simulation, giving scientists their first glimpse below the visible surface.

The international team of scientists, led by the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, say the high-resolution simulations of sunspot pairs open the way for researchers to learn more about the vast, mysterious dark patches on the Sun’s surface. Sunspots are the most striking surface manifestations of solar magnetism, and they are associated with massive ejections of charged plasma that can cause geomagnetic storms and disrupt communications and navigational systems. They also contribute to variations in overall solar output, which can affect weather on Earth and exert a subtle (and as-yet deciphered) influence on climate patterns.

The new research, by scientists at NCAR and the Max Planck Institute for Solar System Research (MPS) in Germany, appears this week in Science Express.

“This is the first time we have a model of an entire sunspot,” says lead author Matthias Rempel, a scientist at NCAR’s High Altitude Observatory. “If you want to understand all the drivers of Earth’s atmospheric system, you have to understand how sunspots emerge and evolve. Our simulations will advance research into the inner workings of the Sun as well as connections between solar output and Earth’s atmosphere.”

Ever since outward flows from the center of sunspots were discovered 100 years ago, scientists have worked toward explaining the complex structure of sunspots, whose number peaks and wanes during the 11-year solar cycle. Sunspots encompass intense magnetic activity that is associated with solar flares and massive ejections of plasma that can buffet Earth’s atmosphere. The resulting damage to power grids, satellites, and other sensitive technological systems takes an economic toll on a rising number of industries.

Creating such detailed simulations would not have been possible even as recently as a few years ago, before the latest generation of supercomputers and a growing array of instruments to observe the Sun. Partly because of such new technology, scientists have already made advances in solving the equations that describe the physics of solar processes.

Source: University Corporation for Atmospheric Research (UCAR), via American Astronomical Society (AAS) press wire

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OK, I admit – the headline is a little over the top. But the sun has been so quiet of late, that even a small sunspot can be exciting. There’s been some debate whether this period of extreme solar calm is truly unusual, or just part of the natural cycle. But solar cycle models never predicted this low amount of activity. “It turns out that none of our models were totally correct,” admitted Dean Pesnell of the Goddard Space Flight Center, a member of an international panel of experts that are now trying to predict what the next solar cycle will hold. “The sun is behaving in an unexpected and very interesting way.”

The panel is predicting that the next cycle, Solar Cycle 24 will have a peak sunspot number of 90, the lowest of any cycle since 1928 when Solar Cycle 16 peaked at 78.


Right now, the solar cycle is in a valley–the deepest of the past century. In 2008 and 2009, the sun set Space Age records for low sunspot counts, weak solar wind, and low solar irradiance. The sun has gone more than two years without a significant solar flare.

“In our professional careers, we’ve never seen anything quite like it,” says Pesnell. “Solar minimum has lasted far beyond the date we predicted in 2007.”

For 2009, the number of “spotless” days are 123, as of May 31, which is 82%.

There’s a little sign of action on the sun, though. In recent months small sunspots and “proto-sunspots” are popping up with increasing frequency. Enormous currents of plasma on the sun’s surface (“zonal flows”) are gaining strength and slowly drifting toward the sun’s equator. Radio astronomers have detected a tiny but significant uptick in solar radio emissions. All these things are precursors of an awakening Solar Cycle 24 and form the basis for the panel’s new, almost unanimous forecast.

According to the forecast, the sun should remain generally calm for at least another year. This calm has a greater affect on Earth’s atmosphere than you might imagine. With low solar activity, the Earth’s atmosphere can cool and contract. Space junk accumulates in Earth orbit because there is less aerodynamic drag; hence the increase in the number of collision event “alarms” for the ISS and shuttles. The calm solar wind whips up fewer magnetic storms around Earth’s poles. Cosmic rays that are normally pushed back by solar wind instead intrude on the near-Earth environment. There are other side-effects, too, that can be studied only so long as the sun remains quiet.

But the sun is a very chaotic place, and even a below-average cycle is capable of producing severe space weather from solar flares and coronal mass ejections (CME) said Doug Biesecker of the NOAA Space Weather Prediction Center. So we shouldn’t be lulled into a false sense of security.

Sources: Science@NASA, SpaceWeather.com

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S-shaped structures called ‘Sigmoids’ have been found in the outer atmosphere of the Sun — the corona. Sigmoids are thought to be a crucial part of explosive events like solar flares. Now a group of astronomers have developed the first model to reproduce and explain the nature of the different stages of a sigmoid’s life. Recently, the X-Ray Telescope (XRT) on board the Hinode space mission was used to obtain the first images of the formation and eruption phase of a sigmoid at high resolution. These observations revealed sigmoids have very complex structures.

Professor Alan Hood and Dr. Vasilis Archontis, both from the Mathematical Institute at St. Andrews University, Scotland, presented their team’s findings today at the European Week of Astronomy and Space Science conference at the University of Hertfordshire.
Over the years a series of theoretical and numerical models have been proposed to explain the nature of sigmoids but until now there was no explanation on how such complex structures form, erupt and fade away. The new model describes how sigmoids consist of many thin and twisted layers (or ribbons) of strong electric current. When these layers interact it leads to the formation of the observed powerful flares and the eruption of strong magnetic fields which carry highly energetic particles into interplanetary space. The team also found that as the sigmoids die out, they produce a ‘flare’ eruption.

Dr. Archontis sees the connection between the two astronomers’ model and work on predicting solar flares. He remarks, “Sigmoids work as ‘mangers’ or ‘cocoons’ for solar eruptions. There is a high probability that they will result in powerful eruptions and other explosive events. Our model helps scientists understand how this happens.”

Prof. Hood adds that these events have real significance for life on Earth, “Sigmoids are among the most interesting features for scientists trying to forecast the solar eruptions – events that can disrupt telecommunications, damage satellites and affect the way navigation systems are operated’.

Explanation of image: This figure shows the time evolution and final eruption of the sigmoid. It consists of three columns (time is running from top to bottom). Columns 1 and 2 show results from numerical experiments. The yellow isosurfaces are surfaces of electric current (left panels). Column 2 (middle panels) shows temperature. Column 3 shows ‘temperature’ (intensity) as it is recorded by the observations (Hinode mission). Notice that the agreement on the shape of the sigmoid, internal structure and thermal distribution along the sigmoid, between numerical experiments and observations is very good and fairly balanced. Notice, that even the ‘flaring’ episode (flashing) at the middle of the sigmoid at the down-right snapshot from observations is reproduced exceptionally well by our numerical experiments (down-middle). Credit: NASA / STFC / ISAS / JAXA / A. Hood (St. Andrews), V. Archontis (St. Andrews)

Source: RAS

Wouldn’t it be great if solar physicists could predict sun storms just like meteorologist predict hurricanes? Well, now perhaps they can. NASA’s twin STEREO observatories have made the first 3-D measurements of solar explosions, known as coronal mass ejections (CMEs), allowing scientists to see their size and shape, and image them as they travel approximately 93 million miles from the sun to Earth. With STEREO, scientists can now capture images of solar storms and make real-time measurements of their magnetic fields, much the same way that satellites allow forecasters to see the development of a hurricane. Eruptions from the sun’s outer atmosphere, or corona, can wreak havoc on satellites (and astronauts) in orbit or induce large currents in power grids on Earth, which can cause power disruptions or black outs.

“We can now see a CME from the time it leaves the solar surface until it reaches Earth, and we can reconstruct the event in 3D directly from the images,” said Angelos Vourlidas, a solar physicist at the Naval Research Laboratory, Washington, and project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation aboard STEREO. In the video above, see some of the 3-D imagery, and hear Vourlidas talk about about the new findings.

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CMEs spew billions of tons of plasma into space at thousands of miles per hour and carry some of the sun’s magnetic field with it. These solar storm clouds create a shock wave and a large, moving disturbance in the solar system. The shock can accelerate some of the particles in space to high energies, a form of “solar cosmic rays” that can be hazardous to spacecraft and astronauts. The CME material, which arrives days later, can disrupt Earth’s magnetic field, or magnetosphere, and upper atmosphere.

STEREO consists of two nearly identical observatories that make simultaneous observations of CMEs from two different vantage points. One observatory ‘leads’ Earth in its orbit around the sun, while the other observatory ‘trails’ the planet. STEREO’s two vantage points provide a unique view of the anatomy of a solar storm as it evolves and travels toward Earth. Once the CME arrives at the orbit of Earth, sensors on the satellites take in situ measurements of the solar storm cloud, providing a “ground truth” between what was seen at a distance and what is real inside the CME.

The combination is providing solar physicists with the most complete understanding to date of the inner workings of these storms. It also represents a big step toward predicting when and how the impact will be felt at Earth. The separation angle between the satellites affords researchers to track a CME in three dimensions, something they have done several times in the past few years as they have learned to use this new space weather tool.

“The in situ measurements from STEREO and other near-Earth spacecraft link the physical properties of the escaping CME to the remote images,” said Antoinette “Toni” Galvin, a solar physicist at the University of New Hampshire, and the principal investigator on STEREO’s Plasma and Suprathermal Ion Composition (PLASTIC) instrument. “This helps us to understand how the internal structure of the CME was formed and to better predict its impact on Earth.”

Until now, CMEs could be imaged near the sun but the next measurements had to wait until the CME cloud arrived at Earth three to seven days later. STEREO’s real-time images and measurements give scientists a slew of information—speed, direction, and velocity—of a CME days sooner than with previous methods. As a result, more time is available for power companies and satellite operators to prepare for potentially damaging solar storms.

Much like a hurricane’s destructive force depends on its direction, size, and speed, the seriousness of a CME’s effects depends on its size and speed, as well as whether it makes a direct or oblique hit across Earth’s orbit.

CMEs disturb the space dominated by Earth’s magnetic field. Disruptions to the magnetosphere can trigger the brightly colored, dancing lights known as auroras, or Northern and Southern Lights. While these displays are harmless, they indicate that Earth’s upper atmosphere and ionosphere are in turmoil.

Sun storms can interfere with communications between ground stations and satellites, airplane pilots, and astronauts. Radio noise from a storm can also disrupt cell phone service. Disturbances in the ionosphere caused by CMEs can distort the accuracy of Global Positioning System (GPS) navigation and, in extreme cases, induce stray electrical currents in long cables and power transformers on the ground.

The twin STEREO spacecraft were launched October 25, 2006, into Earth’s orbit around the sun.

Sources: NASA, APL

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There’s not a lot happening on the sun these days, at least in the sunspot department. “We’re experiencing a very deep solar minimum,” says solar physicist Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, Md. In 2008, no sunspots were observed on 266 of the year’s 366 days (73 percent). Sunspot counts for 2009 have dropped even lower, percentage-wise. As of March 31st, there were no sunspots on 78 of the year’s 90 days (87 percent). Those who keep an eye on the sun say this is the quietest sun in almost a century. So, what does this all mean?

Sunspots are planet-sized islands of magnetism on the surface of the sun, and they are sources of solar flares, coronal mass ejections, and intense UV radiation. The sun has a natural cycle of about 11 years of high and low sunspot activity. This was discovered by German astronomer Heinrich Schwabe in the mid-1800s. Plotting sunspot counts, Schwabe saw that peaks of solar activity were always followed by valleys of relative calm—a clockwork pattern that has held true for more than 200 years.

The current solar minimum is part of that pattern. In fact, it’s right on time. But is it supposed to be this quiet?

Careful measurements by several NASA spacecraft have also shown that the sun’s brightness has dimmed by 0.02 percent at visible wavelengths and a whopping 6 percent at extreme UV wavelengths since the solar minimum of 1996. Radio telescopes are recording the dimmest “radio sun” since 1955.

All these lows have sparked a debate about whether the ongoing minimum is extreme or just an overdue correction following a string of unusually intense solar maxima.

“Since the Space Age began in the 1950s, solar activity has been generally high,” said forecaster David Hathaway of NASA’s Marshall Space Flight Center. “Five of the ten most intense solar cycles on record have occurred in the last 50 years. We’re just not used to this kind of deep calm.”

Deep calm was fairly common a hundred years ago. The solar minima of 1901 and 1913, for instance, were even longer than what we’re experiencing now. To match those minima in depth and longevity, the current minimum will have to last at least another year.

In a way, the calm is exciting, says Pesnell. “For the first time in history, we’re getting to observe a deep solar minimum.” A fleet of spacecraft — including the Solar and Heliospheric Observatory (SOHO), the twin probes of the Solar Terrestrial Relations Observatory (STEREO), and several other satellites — are all studying the sun and its effects on Earth. Using technology that didn’t exist 100 years ago, scientists are measuring solar winds, cosmic rays, irradiance and magnetic fields and finding that solar minimum is much more interesting than anyone expected.

Modern technology cannot, however, predict what comes next. Competing models by dozens of solar physicists disagree, sometimes sharply, on when this solar minimum will end and how big the next solar maximum will be. The great uncertainty stems from one simple fact: No one fully understands the underlying physics of the sunspot cycle.

And the only thing scientists can do it to keep watching. Pesnell believes sunspot counts should pick up again soon, “possibly by the end of the year,” to be followed by a solar maximum of below-average intensity in 2012 or 2013.

Source: NASA