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RE: Solar wind
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With Cluster data, scientists now have evidence that solar outbursts can generate conditions that slingshot matter in Earths magnetic environment to speeds higher than 1000 km/s.

The outburst responsible in a recent study was a Coronal Mass Ejection (CME), a massive cloud of charged particles coming from the Sun. The study compares observations from the four satellites of the ESAs Cluster mission with global simulations of the magnetosphere.
While the Sun continuously loses a small fraction of its mass via the solar wind, a CME is a massive, one-off ejection of matter at high speeds, carrying up to 10 thousand million tonnes of charged particles, or plasma, into the solar system. Most CMEs travelling towards Earth are harmless, but some can affect orbiting satellites or even power grids. Understanding how CMEs impact Earths magnetic environment and consequently space- based and terrestrial technologies is an active field of research.
On 11 January 1997, the 200 million dollar AT&T Telstar 401 satellite suddenly fell silent, cutting TV coverage to millions of viewers. Six days later, after no contact, it was declared permanently out of service. The most likely cause of this failure is that Telstar 401 was hit by a CME.

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Solar Corona
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Title: Turbulence in the Solar Corona
Authors: Steven R. Cranmer (Harvard-Smithsonian CfA)

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but direct observational evidence for a cascade of fluctuation energy from large to small scales is lacking. In this paper I will review the observations of wavelike motions in the corona over a wide range of scales, as well as the macroscopic effects of wave-particle interactions such as preferential ion heating. I will also present a summary of recent theoretical modelling efforts that seem to explain the time-steady properties of the corona (and the fast and slow solar wind) in terms of an anisotropic MHD cascade driven by the partial reflection of low-frequency Alfven waves propagating along the superradially expanding solar magnetic field. Complete theoretical models are difficult to construct, though, because many of the proposed physical processes act on a multiplicity of spatial scales (from centimetres to solar radii) with feedback effects not yet well understood. This paper is thus a progress report on various attempts to couple these disparate scales.

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RE: Solar wind
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solarwind2-enlarged
Image courtesy / ESA and NASA

These are false-colour images of ultraviolet light emitted by the solar atmosphere taken with SOHO's Extreme-ultraviolet Imaging Telescope. Note how more structures appear in the atmosphere as the solar maximum of 2000 approaches, from the left image in early 1997 to the right image in late 1999. These changing structures regulate the escape of helium in the solar wind.

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Helium may act as a "throttle" for the solar wind, setting its minimum speed, according to new results with NASA's Wind spacecraft.
The solar wind is a diffuse stream of electrically conducting gas (plasma) constantly blowing from the sun.

"This result gives us another clue about how the solar wind is accelerated, which may help us better understand space weather" - Dr. Justin Kasper of the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology, Cambridge, Mass., lead author of a paper on this research that appeared in the Astrophysical Journal May 1.

When turbulent solar wind hits Earth's magnetic field, it can cause magnetic storms that overload power lines and radiation storms that disrupt spacecraft.
The new research could also lead to a deeper understanding of plasma physics, which is of interest because stars are made of plasma and plasma is used in advanced devices like plasma TVs and experimental fusion reactors.

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-- Edited by Blobrana at 01:24, 2007-05-18

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Title: The temporal evolution of coronal loops observed by GOES-SXI
Authors: M.C. Lopez Fuentes, J.A. Klimchuk, C.H. Mandrini

We study the temporal evolution of coronal loops using data from the Solar X-ray Imager (SXI) on board of GOES-12. This instrument allows us to follow in detail the full lifetime of coronal loops. The observed light curves suggest three somewhat distinct evolutionary phases: rise, main, and decay. The durations and characteristic timescales of these phases are much longer than a cooling time and indicate that the loop-averaged heating rate increases slowly, reaches a maintenance level, and then decreases slowly. This suggests that a single heating mechanism operates for the entire lifetime of the loop. For monolithic loops, the loop-averaged heating rate is the intrinsic energy release rate of the heating mechanism. For loops that are bundles of impulsively heated strands, it is an indication of the frequency of occurrence of individual heating events, or nanoflares. We show that the timescale of the loop-averaged heating rate is proportional to the timescale of the observed intensity variation. The ratios of the radiative to conductive cooling times in the loops are somewhat less than 1, putting them intermediate between the values measured previously for hotter and cooler loops. Our results provide further support for the existence of a trend suggesting that all loops are heated by the same mechanism, or that different mechanisms have fundamental similarities (e.g., are all impulsive or are all steady with similar rates of heating).

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Satellites and space observatories beware! Microscopic protons are shooting out of the Sun at speeds thousands of times faster than bullets. Although these protons cannot be spotted with the naked eye, they can cause some serious damage.

For example, if enough protons hit a human body, the person could suffer from enough damaged cells that it would make them sick or even kill them. This type of damage has a name: "radiation sickness." Fortunately for living creatures, Earth's atmosphere stops most of the speeding protons coming in from space. The protons just hit air molecules and not human cells.
However, unlike humans, satellites and space observatories, like NASA's Spitzer Space Telescope, aren't so lucky. There is nothing to shelter them from the solar protons zipping around in space. Thus, astronomers on Earth sometimes take extra precautions to protect their space telescopes during solar storms, when large amounts of protons are shot out of the Sun.
What are Protons?
Every atom in the universe has at least one proton, and atoms are the microscopic building blocks of all of the matter we can see, including stars, planets, rocks, and people. Since the Sun is more than a hundred times bigger than the Earth, we know that there are a LOT of atoms with their protons just in the Sun. Astronomers estimate that there are approximately 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 protons living in the Sun. That's a one with 57 zeros following it!

That's more than the total number of grains of sand in the world. In fact, if you had one grain of sand for each proton in the Sun, you could cover the entire surface of the Earth millions of miles deep with sand. You could even pile sand way out past the Moon, which is a quarter of a million miles away.
The Sun is extremely hot, hotter than anything on Earth except the inside of a nuclear explosion. When atoms are heated up that much they come apart and the protons that are usually trapped inside of them are free to fly around at incredible speeds. Although heat may have released protons from the confines of an atom, most are still trapped by the Sun's gravity. However, some of them are fast enough to escape even the Sun's gravity, and race out to the planets and beyond. The fastest protons that leave the Sun fly through space at hundreds or thousands of miles per second.

In every nook and cranny of space between the planets of our solar system, there are solar protons are racing around moment by moment. This is called the "solar wind," because it's like a wind of protons (and electrons) blowing out from the Sun in all directions. Any object in space, be it a spacecraft, an astronaut, or a planet, is getting hit all the time with these. Most of the time there aren't enough of the dangerously fast solar protons leaving the Sun to hurt anything or anybody in space.
But sometimes the Sun has a big explosion on its surface. These eruptions are called "solar storms" when they throw fast protons or electrons out into space. They can produce a lot of dangerous, fast protons that can have speeds as much as 100,000 times faster than bullets. Because of these solar storms, scientists use the term "space weather."
Sometimes during a solar storm, a whole lot of electrons race out from the Sun at high speeds. If lots of solar electrons reach the Earth all at once, it can mess up our electric power lines and even cause power blackouts. In fact, a solar storm event in 1989 almost caused the US one of its worst power blackouts ever, and it did make 6 million people in Quebec lose power for several hours.

Solar storms can sometimes make big parts of interplanetary space fill up with fast protons called a solar "proton event." Solar proton events are the most dangerous space weather event. They are dangerous to both astronauts and spacecraft. Whenever there is a big proton event, the astronauts in the International Space Station hurry to a specially protected part of the station for safety. They wait there until the proton event dies down. A space suit doesn't give enough protection during a big proton event.
Since protons are too small to be seen we can't see them coming, but we can detect them when they get here. There are special proton detectors on several ongoing space missions like SOHO and GOES. These detectors alert us when a big blast of fast protons arrives at Earth, but not before.

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Analysis of the first sample of lunar soil collected by Neil Armstrong has thrown into disarray what researchers believe about the Sun, an international team of scientists says.

Dr Trevor Ireland from the Australian National University and colleagues report in the journal Nature the results of a study of oxygen isotopes on the surface of soil grains returned to Earth by the 1969 Apollo 11 mission.
It was hoped the study would provide clues about the chemical make-up of the Sun and the proto-planetary soup that gave birth to our solar system.
In particular, researchers hoped to find evidence for either of the two reigning theories about the Sun's composition.
According to one theory, the Sun has a similar oxygen composition to the planets.
The other theory suggests it has enriched levels of the isotope oxygen-16.

Instead, the study indicates that while the Sun is dissimilar to bodies like the Earth and meteorites, it has lower levels of oxygen-16 than expected.

"This was a completely unexpected result for us. Our Sun is not the Sun that we thought it was" - Dr Trevor Ireland.

The finding also suggests the Sun somehow ended up with a different composition from the cloud of dust and gas that preceded it. This is based on other small rocky bodies, known as carbonate chondrites, which are the oldest known things in the solar system and have up to 500 times more oxygen-16 than other oxygen isotopes.
While we cannot get samples directly from the Sun, we can infer its composition by looking at lunar samples, which are believed to reflect its composition.
This is because lunar soil contains oxygen isotopes "implanted" by solar winds carrying elements blown out from the Sun.
But after using a caesium beam to erode the surface of the soil grains and measure the isotopes oxygen-16, oxygen-17 and oxygen-18, the researchers discovered unexpectedly low levels of oxygen-16.

"We found that the oxygen ... did not agree with either a planetary composition or the oxygen-16 rich composition. The oxygen isotopes are telling us that the mix of components in the Sun is different to that in the planets, particularly in regard to the amount of dust versus gas that comprises the Sun versus the planets" - Dr Trevor Ireland.

An analysis of oxygen from Jupiter's atmosphere, comets and other bodies in the solar system could shed more light on the mystery.

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RE: Solar neon
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The Chandra X-ray Observatory survey of nearby sun-like stars suggests there is nearly three times more neon in the sun and local universe than previously believed. If true, this would solve a critical problem with understanding how the sun works.

"We use the sun to test how well we understand stars and, to some extent, the rest of the universe. But in order to understand the sun, we need to know exactly what it is made of" - Jeremy Drake of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Mass.

It is not well known how much neon the sun contains. This is critical information for creating theoretical models of the sun. Neon atoms, along with carbon, oxygen and nitrogen, play an important role in how quickly energy flows from nuclear reactions in the sun's core to its edge, where it then radiates into space.

The rate of this energy flow determines the location and size of a crucial stellar region called the convection zone. The zone extends from near the sun's surface inward approximately 125,000 miles. The zone is where the gas undergoes a rolling, convective motion much like the unstable air in a thunderstorm.

"This turbulent gas has an extremely important job, because nearly all of the energy emitted at the surface of the sun is transported there by convection" - Jeremy Drake .



These Chandra results reassured astronomers the detailed physical theory behind the solar model is secure. Scientists use the model of the sun as a basis for understanding the structure and evolution of other stars, as well as many other areas of astrophysics.

Neon, along with atoms of carbon, nitrogen and oxygen, plays an important role in regulating the rate at which energy flows from nuclear reactions in the Sun's core to its surface. The character of the energy flow changes dramatically about 125,000 miles from the surface on the Sun, where the stately diffusion of heat suddenly converts to a convective motion much like the unstable air in a thunderstorm.

The location of this turbulent region, called the convection zone, has been deduced to fairly high precision from the study of oscillations of the surface of the Sun (a technique called helioseismology in analogy of the use of oscillations of the Earth to study its interior). The location of the convection zone can also be deduced to equal precision from theoretical calculations based on among other things, the abundance of neon.

This is where astrophysicists get heartburn. The two determinations disagree. Several scientists have proposed that the paradox could be resolved if the solar abundance of neon is in fact about three times larger than the currently accepted value. This value is based on indirect estimates, since gas at the relatively cool 6,000 degree Celsius surface temperature of the Sun gives off no characteristic radiation at optical wavelengths.
However, a gas heated to millions of degrees produces a distinct neon signal in X-rays. The upper atmospheres, or coronas, of stars like the Sun have temperatures of millions of degrees, so the solar corona would seem to be a good place to settle the argument (not with Chandra - the bright solar radiation would irreparably damage the telescope).
Unfortunately, the solar X-rays come from numerous localized loops of hot gas that vary from location to location and time to time, complicating the interpretation of the data on neon. Jeremy Drake of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, MA and his colleague Paola Testa of the Massachusetts Institute of Technology in Cambridge, came up with an ingenious approach to the problem. They used Chandra to measure the neon abundance in 21 Sun-like stars within a distance of 400 light years.



The relative amount of neon in these stars was, on average, almost three times more neon than is measured for the Sun, just the amount needed to bring the solar oscillation observations and the theoretical model into agreement.
So, for the moment, astrophysicists can feel that their model of the Sun may be okay after all, and they can continue to boldly extrapolate this understanding to the rest of the Universe.

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The Sun may contain three times more neon than previously thought, according to a new study.
The finding may solve a theoretical problem regarding how stars in general work.

"Understanding the way the Sun works is the bottom rung in a ladder to understanding how the rest of the universe works" - Jeremy Drake of the Harvard-Smithsonian Centre for Astrophysics.

In the past, astrophysicists based their solar model on data collected from studies that measured the way pressure waves propagate throughout the Sun.
The model was put into question, however, when their value for the neon abundance in the Sun differed from those calculated using other techniques.
One of these techniques involved capturing particles from the solar wind, a stream of charged particles that continuously streams from the Sun, and tallying up the total number and type of atoms present from each element.
Another involved X-rays; neon does not appear in the visible spectrum of light but it shines brightly in X-rays.

Based on these techniques, astronomers came up with a value for the Sun's neon concentration that differed from the value used in the astrophysicist's model by a factor of three.

"When astrophysicists plugged in these new values, their model broke" - Jeremy Drake.

Drake said the disagreement about the concentration of neon may have been due to problems with both the solar wind technique and the X-ray method.
In the case of the solar wind, the Sun accelerates a particle differently depending on its mass and charge, which vary from element to element.
With X-rays, the problem is one of distance. Because Earth is relatively close to the Sun, scientists can't look at the solar furnace in its entirety, and must instead settle for examining different parts separately.

When viewed from such a close distance, different elements appear in different concentrations in different parts of the Sun, Drake explained, and it is difficult to say which area, if any, is an accurate representation of the Sun's chemical makeup.
Drake and his colleague Paola Testa from the Massachusetts Institute of Technology got around these problems by measuring the neon abundance of 21 nearby Sun-like stars using NASA's Chandra X-ray Observatory.

By taking a distant look, they measured the average X-ray emission from the stars.
What the researchers found was that the nearby stars contained three times more neon than was calculated for the Sun.

The implication was clear. "Either the Sun is a freak in its stellar neighbourhood, or it contains a lot more neon than we think" - Paola Testa, Massachusetts Institute of Technology and another study team member.

Drake said the same technique could be used on our own Sun, if not for one problem: the detectors on Chandra's instruments would fry because of the heat.
The study will be detailed in the July 28 issue of the journal Nature.

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New research from the National Centre for Atmospheric Research (NCAR) links a particular magnetic structure on the Sun with the genesis of powerful solar storms that can buffet Earth's atmosphere. The research may enable scientists to create more accurate computer models of the solar storms, known as coronal mass ejections (CMEs), and could eventually point the way to forecasting the storms days before they occur.
Sarah Gibson, a scientist at NCAR's High Altitude Observatory (HAO), presented her findings at the American Geophysical Union conference in New Orleans on Thursday.
Her invited talk was in recognition of winning this year's Karen Harvey Prize. Awarded by the Solar Physics Division of the American Astronomical Society, the prize recognizes an early-career scientist who has produced exceptional solar research.


Sarah Gibson struck a pose for the camera as she gazed at her first solar eclipse in 1991. Behind her on the far left is NCAR's Mauna Loa Solar Observatory, the home of state-of-the-art Coronametres to capture detailed images of the Sun's outermost region.

CMEs are a focus of solar research because they suddenly and violently release billions of tons of matter and charged particles that escape from the Sun and speed through space. Ejections pointed toward Earth can set off disturbances when they reach the upper atmosphere, affecting satellites, ground-based communications systems, and power grids.
For her research, Gibson turned to a unique data set: white-light images of the lower reaches of the Sun's enormous halo, called the corona. Taken by NCAR's Mark-IV K-Coronameter on Mauna Loa in Hawaii, the images are sensitive to density alone, avoiding the ambiguity of most other solar images that depend on both temperature and density. The images revealed that lower-density regions in the corona consistent with twisted magnetic field lines can form prior to a CME. The twisted areas, known as magnetic flux ropes, store massive amounts of energy.


Watch an animation of the November 19 coronal mass ejection.

"The structures indicate a magnetic system that has enough energy to fuel a CME. But their presence is not, by itself, an indication that a CME is about to occur. For that, we need to look at additional characteristics." - Sarah Gibson.

The research may put to rest an important debate among solar physicists over whether magnetic flux ropes can form prior to an ejection or are merely present when an ejection takes place. Gibson's findings suggest that, to understand the forces that create CMEs, solar scientists should use magnetic flux ropes as starting points for computer models of the massive storms.

To conduct her study, Gibson used Mark-IV images to observe dark, lower-density areas, known as cavities, which can be formed by the strong, sheared magnetic fields of magnetic flux ropes. She and NCAR colleagues analyzed 13 cavity systems from November 1999 to January 2004. Seven of these systems could be associated with CMEs, and four cavities were directly observed by the Coronameter to erupt as CMEs. Gibson used a second technique to identify an additional eight CMEs that erupted from already-formed cavities. She found those cases by gathering images of CMEs and backtracking to see whether cavities existed at those CME sites before each eruption.

One of Gibson's next steps will be to analyze cavities that result in CMEs to determine whether they have identifiable characteristics that may help scientists forecast a CME. Her preliminary findings indicate that a cavity begins to bulge and rise higher in the corona just before erupting. Cavities may also darken and become more sharply defined prior to eruption.
Gibson will also try to determine how widespread cavities are, and if it is possible that most, or even all, CMEs are preceded by the formation of magnetic flux ropes. Beginning next year, she will supplement the Mauna Loa observations with data from a pair of new NASA satellites, known as STEREO (Solar Terrestrial Relations Observatory). Instruments aboard STEREO will provide stereoscopic measurements and 24-hour coverage of the lower solar corona, significantly increasing the chances of directly observing cavities erupting into CMEs.

(source)

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