Naked Science Forum
Life Sciences => The Environment => Topic started by: frethack on 23/06/2009 16:58:56
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This might belong in the Physics, Astronomy and Cosmology section, but it has climate implications as well. Looks like we may finally see the solar cycle ramping up.
http://solarscience.auditblogs.com/2009/06/17/nasa-the-mystery-of-the-missing-sunspots-solved/ (http://solarscience.auditblogs.com/2009/06/17/nasa-the-mystery-of-the-missing-sunspots-solved/)
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Sunspots Revealed in Striking Detail by Supercomputers
http://www.earthtoday.net/news/viewpr.rss.html?pid=28491
In a breakthrough that will help scientists unlock mysteries of the Sun and its impacts on Earth, an international team of scientists led by the National Center for Atmospheric Research (NCAR) has created the first-ever comprehensive computer model of sunspots. The resulting visuals capture both scientific detail and remarkable beauty.
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 manifestations of solar magnetism on the solar surface, 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 influence on climate patterns.
The research, by scientists at NCAR and the Max Planck Institute for Solar System Research (MPS) in Germany, is being published 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 made advances in solving the equations that describe the physics of solar processes.
The work was supported by the National Science Foundation, NCAR's sponsor. The research team improved a computer model, developed at MPS, that built upon numerical codes for magnetized fluids that had been created at the University of Chicago.
--- Computer Model Provides a Unified Physical Explanation ---
The new computer models capture pairs of sunspots with opposite polarity. In striking detail, they reveal the dark central region, or umbra, with brighter umbral dots, as well as webs of elongated narrow filaments with flows of mass streaming away from the spots in the outer penumbral regions. They also capture the convective flow and movement of energy that underlie the sunspots, and that are not directly detectable by instruments.
The models suggest that the magnetic fields within sunspots need to be inclined in certain directions in order to create such complex structures. The authors conclude that there is a unified physical explanation for the structure of sunspots in umbra and penumbra that is the consequence of convection in a magnetic field with varying properties.
The simulations can help scientists decipher the mysterious, subsurface forces in the Sun that cause sunspots. Such work may lead to an improved understanding of variations in solar output and their impacts on Earth.
--- Supercomputing at 76 Trillion Calculations per Second ---
To create the model, the research team designed a virtual, three-dimensional domain that simulates an area on the Sun measuring about 31,000 miles by 62,000 miles and about 3,700 miles in depth - an expanse as long as eight times Earth's diameter and as deep as Earth's radius. The scientists then used a series of equations involving fundamental physical laws of energy transfer, fluid dynamics, magnetic induction and feedback, and other phenomena to simulate sunspot dynamics at 1.8 billion points within the virtual expanse, each spaced about 10 to 20 miles apart. For weeks, they solved the equations on NCAR's new bluefire supercomputer, an IBM machine that can perform 76 trillion calculations per second.
The work drew on increasingly detailed observations from a network of ground- and space-based instruments to verify that the model captured sunspots realistically.
The new models are far more detailed and realistic than previous simulations that failed to capture the complexities of the outer penumbral region. The researchers noted, however, that even their new model does not accurately capture the lengths of the filaments in parts of the penumbra. They can refine the model by placing the grid points even closer together, but that would require more computing power than is currently available.
"Advances in supercomputing power are enabling us to close in on some of the most fundamental processes of the Sun," says Michael Knolker, director of NCAR's High Altitude Observatory and a co-author of the paper. "With this breakthrough simulation, an overall comprehensive physical picture is emerging for everything that observers have associated with the appearance, formation, dynamics, and the decay of sunspots on the Sun's surface."
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Sonograms of the Sun Explain Mystery of the Missing Sunspots
http://www.earthtoday.net/news/viewpr.rss.html?pid=28518
Boulder, Colorado -- Scientists from the National Solar Observatory (NSO) in Tucson, Arizona, have discovered that a solar jet stream deep inside the Sun is migrating slower than usual through the star's interior, giving rise to the current lack of sunspots and low solar activity, according to work being presented this week at the meeting of the Solar Physics Division of the American Astronomical Society (AAS/SPD).
The Sun normally undergoes an eleven-year cycle of magnetic activity related to sunspots, solar flares, and the interplanetary storms called "CMEs". The current "solar minimum" quiet period has been unusually long and deep, confounding scientists who hope to understand the origins of space weather and the Sun's magnetic field.
Drs. Rachel Howe and Frank Hill, both of the NSO, used long-term observations from the NSO's Global Oscillation Network Group (GONG) facility to detect and track an east-to-west jet stream, known as the "torsional oscillation", at depths of ~1,000 to 7,000 km below the surface of the Sun. The Sun generates new jet streams near its poles every 11 years; the streams migrate slowly, over a period of 17 years, to the equator, and are associated with the production of sunspots once they reach a critical latitude of 22 degrees.
Howe and Hill found that the stream associated with the new solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to two years for the last solar cycle, but has now reached the critical latitude. The current solar minimum has become so long and deep, some scientists have speculated the Sun might enter a long period with no sunspot activity at all. The new result both shows that the Sun's internal magnetic dynamo continues to operate, and heralds the beginning of a new cycle of solar activity.
Images online at http://spd.boulder.swri.edu/solar_mystery/
"It is exciting to see", said Dr. 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 at the new active latitude." Since the current minimum is now one year longer than usual, Howe and Hill conclude that the extended solar minimum phase may have resulted from the slower migration of the flow.
GONG and its sister instrument SOHO/MDI measure sound waves on the surface of the Sun. Scientists can then use the sound waves to probe structures deep in the interior of the star, in a process analogous to a sonogram in a medical office. "Using the global sound wave inversions, we have been able to reveal the intimate connection between subtle changes in the Sun's interior and the sunspot cycle on its surface," said Hill.
"This is an important piece of the solar activity puzzle," said Dr. Dean Pesnell, of NASA's Goddard Space Flight Center. "It shows how flows inside the Sun are related to the creation of solar activity and how the timing of the solar cycle might be produced. None of the forecasting research groups predicted the current long extended delay in the new cycle. There is a lot more to learn in order to understand how the Sun creates magnetic fields."
The new science of helioseismology, enabled by instruments such as the ground- based GONG, the Michelson Doppler Imager aboard the SOHO spacecraft, and NASA's planned Solar Dynamics Observatory, has revolutionized understanding of the solar interior. "While the surface effects of the Sun's torsional oscillations have been observed for some time, understanding of the dynamo and the origin of sunspots depend on measurements of the solar interior that are only possible with helioseismic techniques", said Hill.