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 Solar Storms can Change Directions, Surprising Forecasters 
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Post Solar Storms can Change Directions, Surprising Forecasters
Solar Storms can Change Directions, Surprising Forecasters

Sept. 21, 2010: Solar storms don't always travel in a straight line. But once they start heading in our direction, they can accelerate rapidly, gathering steam for a harder hit on Earth's magnetic field.

So say researchers who have been using data from NASA's twin STEREO spacecraft to unravel the 3D structure of solar storms. Their findings are presented in today's issue of Nature Communications.


Image


"This really surprised us," says co-author Peter Gallagher of Trinity College in Dublin, Ireland. "Solar coronal mass ejections (CMEs) can start out going one way—and then turn in a different direction."

The result was so strange, at first they thought they'd done something wrong. After double- and triple-checking their work on dozens of eruptions, however, the team knew they were onto something.

"Our 3D visualizations clearly show that solar storms can be deflected from high solar latitudes and end up hitting planets they might otherwise have missed," says lead author Jason Byrne, a graduate student at the Trinity Center for High Performance Computing.


A 3D model of an actual CME based on multiscale processing of STEREO data. [9MB movie] The key to their analysis was an innovative computing technique called "multiscale image processing." Gallagher explains:

"'Multiscale processing' means taking an image and sorting the things in it according to size. Suppose you're interested in race cars. If you have a photo that contains a bowl of fruit, a person, and a dragster, you could use multiscale processing to single out the race car and study its characteristics."

In medical research, multiscale processing has been used to identify individual nuclei in crowded pictures of cells. In astronomy, it comes in handy for picking galaxies out of a busy star field. Gallagher and colleagues are the first to refine and use it in the realm of solar physics.

"We applied the multiscale technique to coronagraph data from NASA's twin STEREO spacecraft," Gallagher continues. "Our computer was able to look at starry images cluttered with streamers and bright knots of solar wind and zero in on the CMEs."

STEREO-A and STEREO–B are widely separated and can see CMEs from different points of view. This allowed the team to create fully-stereoscopic models of the storm clouds and track them as they billowed away from the sun.

One of the first things they noticed was how CMEs trying to go "up"—out of the plane of the solar system and away from the planets—are turned back down again. Gallagher confesses that they had to "crack the books" and spend some time at the white board to fully understand the phenomenon. In the end, the explanation was simple:


The magnetic field of a bar magnet. The sun's global magnetic field, which is shaped like a bar magnet, guides the wayward CMEs back toward the sun's equator. When the clouds reach low latitudes, they get caught up in the solar wind and head out toward the planets—"like a cork bobbing along a river," says Gallagher.

Once a CME is embedded in the solar wind, it can experience significant acceleration. "This is a result of aerodynamic drag," says Byrne. "If the wind is blowing fast enough, it drags the CME along with it—something we actually observed in the STEREO data."

Past studies from other missions had revealed tantalizing hints of this CME-redirection and acceleration process, but STEREO is the first to see it unfold from nearly beginning to end.

"The ability to reconstruct the path of a solar storm through space could be of great benefit to forecasters of space weather at Earth," notes Alex Young, STEREO Senior Scientist at the Goddard Space Flight Center. "Knowing when a CME will arrive is crucial for predicting the onset of geomagnetic storms."

"Furthermore," he says, "the image processing techniques developed by the Trinity team in collaboration with NASA Goddard can be used in applications ranging from surveillance to medical diagnostics."

Snip

http://science.nasa.gov/science-news/science-at-nasa/2010/21sep_zigzag/



:huh

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Thu Sep 23, 2010 4:39 am
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Post Re: Solar Storms can Change Directions, Surprising Forecasters
The Science behind this observation:


Propagation of an Earth-directed coronal mass ejection in three dimensions


Introduction

Coronal mass ejections (CMEs) are spectacular eruptions of plasma and magnetic field from the surface of the Sun into the heliosphere. Travelling at speeds of up to 2,500 km s−1 and with masses of up to 1016 g, they are recognized as drivers of geomagnetic disturbances and adverse space weather on Earth and on other planets in the solar system1, 2. Affecting our magnetosphere with average magnetic field strengths of 13 nT and energies of ~1025 J, they can cause telecommunication and Global Positioning System (GPS) errors, power grid failures and increased radiation risks to astronauts3. It is therefore important to understand the forces that determine their evolution, in order to better forecast their arrival time and impact on Earth and throughout the heliosphere.

Identifying the specific processes that trigger the eruption of CMEs is the subject of much debate, and many different models exist to explain these4, 5, 6. One common feature is that magnetic reconnection is responsible for the destabilization of magnetic flux ropes on the Sun, which then erupt through the corona into the solar wind to form CMEs7. In the low solar atmosphere, it is postulated that high-latitude CMEs undergo deflection as they are often observed at different position angles than their associated source region locations8. It has been suggested that field lines from polar coronal holes may guide high-latitude CMEs towards the equator9, or that the initial magnetic polarity of a flux rope relative to the background magnetic field influences its trajectory10, 11. During this early phase, CMEs are observed to expand outwards from their launch site, although plane-of-sky measurements of their increasing sizes and angular widths are ambiguous in this regard12. This expansion has been modelled as being due to a pressure gradient between the flux rope and the background solar wind13, 14. At larger distances in their propagation, CMEs are expected to interact with the solar wind and the interplanetary magnetic field. Studies that compare in situ CME velocity measurements with initial eruption speeds through the corona show that slow CMEs are accelerated towards the speed of the solar wind, and fast CMEs decelerated15, 16. It has been suggested that this is due to the effects of drag on the CME in the solar wind17, 18. However, the quantification of drag, along with that of both CME expansion and non-radial motion, is currently lacking, primarily because of the limits of observations from single fixed viewpoints with restricted fields of view. The projected two-dimensional nature of these images introduces uncertainties in kinematical and morphological analyses, and therefore the true three-dimensional (3D) geometry and dynamics of CMEs have been difficult to resolve. Efforts were made to infer 3D structure from two-dimensional images recorded by the large angle spectrometric coronagraph on board the Solar and Heliospheric Observatory, situated at the first Lagrangian point (L1), at which its orbital motion around the Sun is synchronous with that of the Earth's. These efforts were based on either a preassumed geometry of the CME19, 20, 21 or a comparison of observations with in situ and on-disk data22, 23. Of note is the polarization technique used to reconstruct the 3D geometry of CMEs in large angle spectrometric coronagraph data24, although this is only valid for heights of up to 5 R (1R= 6.95x10^5 km ).

Snip


CME Observation

On 12 December 2008, an erupting prominence was observed by STEREO while the spacecraft was in near quadrature at 86.7° separation (Fig. 1a). The eruption were visible at 50–55° north from 03:00 UT in SECCHI/Extreme Ultraviolet Imager (EUVI) images, obtained in the 304 Å passband, in the northeast from the perspective of STEREO-(A)head and off the northwest limb from STEREO-(B)ehind. The prominence is considered to be the inner material of the CME, which was first observed in COR1-B at 05:35 UT (Fig. 1b). For our analysis, we use the two coronagraphs (COR1/2) and the inner HI1 (Fig. 1c). We characterize the propagation of the CME across the plane of sky by fitting an ellipse to the front of the CME in each image38 (Supplementary Movie 1). This ellipse fitting is applied to the leading edges of the CME but equal weight is given to the CME flank edges as they enter the field of view of each instrument. The 3D reconstruction is then performed using a method of elliptical tie pointing within epipolar planes containing the two STEREO spacecraft, illustrated in Figure 2 (see Methods section).


Image

Figure 1: Composite of STEREO-A and B images from the SECCHI instruments of the CME of 12 December 2008.

(a) Indicates the STEREO spacecraft locations, separated by an angle of 86.7° at the time of the event. (b) Shows the prominence eruption observed in EUVI-B off the northwest limb from approximately 03:00 UT, which is considered to be the inner material of the CME. The multiscale edge detection and corresponding ellipse characterization are overplotted in COR1. (c) Shows that the CME is Earth-directed, being observed off the east limb in STEREO-A and off the west limb in STEREO-B.


Figure 2: Epipolar geometry used to constrain the reconstruction of the CME front.

Image


The reconstruction is performed using an elliptical tie-pointing technique within epipolar planes containing the two STEREO spacecraft27. For example, one of any number of planes will intersect the ellipse characterization of the CME at two points in each image from STEREO-A and B. (a) Illustrates how the resulting four sight lines intersect in 3D space to define a quadrilateral that constrains the CME front in that plane56, 57. Inscribing an ellipse within the quadrilateral such that it is tangent to each sight line58, 59 provides a slice through the CME that matches the observations from each spacecraft. (b) Illustrates how a full reconstruction is achieved by stacking multiple ellipses from the epipolar slices. As the positions and curvatures of these inscribed ellipses are constrained by the characterized curvature of the CME fronts in the stereoscopic image pair, the modelled CME front is considered to be an optimum reconstruction of the true CME front. (c) Illustrates how this is repeated for every frame of the eruption to build the reconstruction as a function of time and view the changes to the CME front as it propagates in 3D. Although the ellipse characterization applies to both the leading edges and, when observable, the flanks of the CME, only the outermost part of the reconstructed front is shown here for clarity, and illustrated in Supplementary Movie 2.

Snip


The whole article is Here


:sherlock

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Thu Sep 23, 2010 4:51 am
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Post Re: Solar Storms can Change Directions, Surprising Forecasters
Another great post Sky thanks :clap :clap :clap

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Thu Sep 23, 2010 5:30 am
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Post Re: Solar Storms can Change Directions, Surprising Forecasters
This article really tickled my fancy L2L!

I find it incredible that they have been observing the Sun for how long, and they only tell about this now. :censor

Whoha! I think there will be more "buns in the oven" that will be exposed soon. But then we should not be surprised by the source - should we?


:gah

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Thu Sep 23, 2010 6:04 am
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Post Re: Solar Storms can Change Directions, Surprising Forecasters
Wow, Sky! This is soooo interesting - not only the science but the timing as well. :hmm

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Thu Sep 23, 2010 6:09 am
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Post Re: Solar Storms can Change Directions, Surprising Forecasters
My sentiments too BB. If you watch the news relating to the Sun, and the "Climate Change" leaks from world Scientists/Govt's/PTB's you will notice a sort-off ramping effect. I think they are starting to "feel" the cracks developing and are either trying to clean their slates re STO options or being politically correct for what will be a sure backlash from the public.

But that is jest my lil' ol' opinion!


:whistle

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