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TOPIC: The Sun
Blobrana


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RE: The Sun
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Scientists may have at last found a way to explore the heart of the sun with the detection of a special type of wave generated deep in the solar interior. The heart, or core, of the sun is the location of the sun's nuclear furnace, where fusion reactions power the sunlight that supports almost all life on Earth.
The Solar and Heliospheric Observatory (SOHO) spacecraft may have glimpsed these waves in the form of ripples on the suns surface. Analysis of the ripples will reveal details about the hidden core of our central star. Such information contains clues about how the Sun formed, 4.6 billion years ago.

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-- Edited by Blobrana at 20:08, 2007-05-14

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Blobrana


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Astronomers using the Global Oscillation at Low Frequency (GOLF) instrument on SOHO think they may have caught glimpses of this behaviour. Instead of looking for an individual oscillation, they looked for the signature of the cumulative effect of a large number of these oscillations.
As an analogy, imagine that the Sun was an enormous piano playing all the notes simultaneously. Instead of looking for a particular note (middle C for instance) it would be easier to search for all the Cs, from all the octaves together.
In the piano their frequencies are related to each other just as on the Sun, one class of g modes are separated by about 24 minutes.

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Blobrana


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g-modes
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The ESA-NASA Solar and Heliospheric Observatory (SOHO) may have glimpsed long-sought oscillations on the Sun's surface. The data will reveal details about the very core of our central star and it contains clues as to how the Sun formed, 4.6 billion years ago.
The subtle variations reveal themselves as a minuscule ripple in the overall movement of the solar surface. Astronomers have been searching for ripples of this kind since the 1970s, when they first detected that the solar surface was oscillating in and out.
The so-called 'g-modes' are driven by gravity and provide information about the deep interior of the Sun. They are thought to occur when gas churning below the solar surface plunges even deeper into our star and collides with denser material, sending ripples propagating through the Sun's interior and up to the surface. It is the equivalent of dropping a stone in a pond.

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Blobrana


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The sun in 3 dimension taken in 2007 by the  STEREO "A" and "B" spacecrafts

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Blobrana


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GIANT PIPE ORGAN IN THE SOLAR ATMOSPHERE
Astronomers have found that the atmosphere of the Sun plays a kind of heavenly music. The magnetic field in the outer regions (the corona) of our nearest star forms loops that carry waves and behave rather like a musical instrument. In a talk on Thursday 19 April at the Royal Astronomical Society National Astronomy Meeting in Preston, Dr Youra Taroyan and Professor Robert von Fay-Siebenburgen of the Solar Physics and Space Plasma Research Centre (SP2RC), University of Sheffield will explain the origin of these magnetic sound waves. They will present a series of animations and sound files that demonstrate how these dramatic events appear and fade away rapidly.
In recent years scientists have worked hard to better explain and predict the dynamic behaviour of the Sun. For example, missions like STEREO and Hinode watch as material is ejected towards the Earth, events which are controlled by the solar magnetic field.
In their research, led by Professor von Fay-Siebenburgen, SP2RC scientists combined observations with new theoretical models to study the magnetic sound waves that are set up along loops in the corona.

"These loops can be up to 100 million kilometres long and guide waves and oscillations in a similar way to a pipe organ" - Dr Youra Taroyan.

The acoustic waves can be extremely powerful and reach amplitudes of tens of kilometres per second.

"We found that the waves are often generated at the base of the magnetic pipes by enormous explosions known as micro-flares. These release energy equivalent to millions of hydrogen bombs. After each micro-flare, sound booms are rapidly excited inside the magnetic pipes before decaying in less than an hour and dissipating in the very hot solar corona" - Professor von Fay-Siebenburgen.

Source RAS

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Blobrana


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X-ray images taken by the Hinode Satellite show that the sun's magnetic field is much more turbulent than scientists knew, NASA reported Wednesday.
They saw twisting plumes of gas rising from the sun's corona and reacting with the star's magnetic field, a process that releases energy and may power solar storms and coronal mass ejections, which in turn affect the Earth. A turbulent magnetic field would, in theory, generate more energy than a steady-state field.

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Blobrana


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11-year sunspot cycle
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Although very close to the minimum of its 11-year sunspot cycle, the Sun showed that it is still capable of producing a series of remarkably energetic outbursts - ESA-NASA Ulysses mission revealed.
 In keeping with the first and second south polar passes (in 1994 and 2000), the latest high-latitude excursion of the joint ESA-NASA Ulysses mission has already produced some surprises. In mid-December 2006, although very close to the minimum of its 11-year sunspot cycle, the Sun showed that it is still capable of producing a series of remarkably energetic outbursts.
The solar storms, which were confined to the equatorial regions, produced quite intense bursts of particle radiation that were clearly observed by near-Earth satellites. Surprisingly, similar increases in radiation were detected by the instruments on board Ulysses, even though it was three times as far away and almost over the south solar pole.

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Blobrana


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Title: Observations and Simulations of Fibrils and Mottles
Authors: Bart De Pontieu (1), Viggo H. Hansteen (2), Luc Rouppe van der Voort (2), Michiel van Noort (3), Mats Carlsson (2) ((1) Lockheed Martin Solar & Astrophysics Lab, Palo Alto, CA, USA, (2) Institute for Theoretical Astrophysics, Oslo, Norway, (3) Institute for Solar Physics of the Royal Swedish Academy of Sciences, Sweden)

With the recent advent of the Swedish 1-m Solar Telescope (SST), advanced image processing techniques, as well as numerical simulations that provide a more realistic view of the chromosphere, a comprehensive understanding of chromospheric jets such as spicules, mottles and fibrils is now within reach. In this paper, we briefly summarize results from a recent analysis of dynamic fibrils, short-lived jet-like features that dominate the chromosphere (as imaged in H-alpha) above and about active region plage. Using extremely high-resolution observations obtained at the SST, and advanced numerical 2D radiative MHD simulations, we show that fibrils are most likely formed by chromospheric shock waves that occur when convective flows and global oscillations leak into the chromosphere along the field lines of magnetic flux concentrations. In addition, we present some preliminary observations of quiet Sun jets or mottles. We find that the mechanism that produces fibrils in active regions is most likely also at work in quiet Sun regions, although it is modified by the weaker magnetic field and the presence of more mixed-polarity. A comparison with numerical simulations suggests that the weaker magnetic field in quiet Sun allows for significantly stronger (than in active regions) transverse motions that are superposed on the field-aligned, shock-driven motions. This leads to a more dynamic, and much more complex environment than in active region plage. In addition, our observations of the mixed polarity environment in quiet Sun regions suggest that other mechanisms, such as reconnection, may well play a significant role in the formation of some quiet Sun jets.

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Blobrana


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The prototype of a new solar patrol telescope in New Mexico recorded a tsunami-like shock wave rolling across the visible face of the Sun following a major flare even on Wednesday, Dec. 6, 2006, at 18:28 Universal Time (11:28 MST). The shock wave, known as a Moreton wave, also destroyed or compressed two filaments of cool gas at opposite sides of the solar hemisphere.

"These large scale 'blast' waves occur infrequently, however, are very powerful. They quickly propagate in a matter of minutes covering the whole Sun, sweeping away filamentary material. It is unusual to see such powerful waves encompassing the whole sun from ground based observatories. Its significance comes from the fact that these waves are occurring near solar minimum, when intense activity is yet to pick up" - Dr. K. S. Balasubramaniam, of the National Solar Observatory (NSO) in Sunspot, NM, who is studying these and other phenomena.

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Blobrana


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Sunspots
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Title: A Look into the Guts of Sunspots
Authors: L.R. Bellot Rubio (IAA/CSIC, Granada)

Advances in instrumentation have made it possible to study sunspots with unprecedented detail. New capabilities include imaging observations at a resolution of 0.1" (70 km on the sun), spectroscopy at ~0.2", and simultaneous spectropolarimetry in visible and infrared lines at resolutions well below 1". In spite of these advances, we still have not identified the building blocks of the penumbra and the mechanism responsible for the Evershed flow. Three different models have been proposed to explain the corpus of observations gathered over the years. The strengths and limitations of these models are reviewed in this contribution.

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