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The solar corona unveiled


The SWAP instrument aboard ESA’s mission PROBA2 captures new images of the solar corona outside. The findings could explain the unusual activity of the solar cycle 24.
The mission PROBA2 ESA gives us new and exciting information on the solar corona observed in the band of the extreme ultraviolet. The data reveal a structure mysteriously beautiful and soft, which extends up to extraordinarily regions far from the sun. The video made with images captured by the SWAP instrument of the Royal Observatory of Belgium, aboard PROBA2, have allowed us to observe unusual filamentous structures in region where the solar wind is accelerated. The results were presented yesterday at the Triennial Earth-Sun Summit, the meeting of the Solar Physics Division of the American Astronomical Society and the Section of Space Physics and Aeronomy of the American Geophysical Union that is taking place this week in Indianapolis.

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Credit: Royal Observatory of Belgium

The images in the extreme ultraviolet crown dynamics of the Sun, with its eruptions and the reticle of magnetic rings, have become familiar through space telescopes, such as the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO). But new data from the telescope on SWAP PROBA2, a mini-European satellite launched in November of 2009, reveal a new and surprising behavior of this region. If on the one hand SWAP confirms the presence of the magnetic rings of the lower crown, the new observations show that the above characteristics of these structures there is a region dominated by soft structures in filaments that wrap around the rings in the background of the crown and extending towards the ‘external and in interplanetary space.
While we know that the low corona is dominated by dynamic events such as solar flares, which can heat the surrounding plasma to tens of millions of degrees, the new observations from SWAP reveal the presence of a region with an evolution much slower and stable where does the connection between the Sun itself and the solar wind that fills interplanetary space. The observations reveal structures of SWAP fan-shaped surprisingly long-lived, which extend to a height greater than 700,000 km above the Sun’s surface. These structures, in some cases, are even larger than the Sun itself. Understand what physical processes are responsible for the formation of these structures is the key to determine the nature of the complex relationship between the corona and the solar wind.
“Over the past years, SWAP has observed an increasing number of these structures in a fan that extend up to one million kilometers from the Sun,” said Daniel Seaton, scientist responsible for the instrument SWAP at the Royal Observatory of Belgium. “These filamentary structures are linked to other structures that are observed to even greater heights in white light images from coronagraphs or eclipse, but seem to behave very differently. Sometimes they fold towards the poles solar and wind around the intense beams of magnetic field to which it hooks the solar plasma protuberances called ‘.
Watching movies in time-lapse images of the instrument to SWAP, the effect is amazing, and reveals a crown lively, very different from what solar physicists have observed so far.
The new observations could also provide clues to unravel the behavior of the cycle of magnetic activity of the Sun, a cycle lasting 22 years which in recent years has repeatedly denied the expectations of scientists. Typically, the Sun goes through an evolution magnetic extremely predictable: from quiet to active, and back to the starting point. The current cycle has grown slowly and has not been active since the previous cycles. At the same time, the northern and southern hemispheres of the Sun, which typically evolve in a fairly independent, have become almost completely decoupled.
The films collected by SWAP showing the long-term evolution of the crown during the growth phase of the solar cycle 24 reveal clear links both with the number of sunspots, a key indicator of solar activity, both with the activities of discordant two hemispheres. Strangely, the activity of the low solar atmosphere has been largely dominated by a single hemisphere, the north, whose activity is also manifested at large distances from the Sun’s surface. The analysis of the structures in a fan that dominate the observations of SWAP revealed some of the reasons of their appearance, which has been linked to the increase in solar activity over the past five years. The analysis also helps to explain why these filaments sometimes disappear from observations.
“These coronal structures visible in the far ultraviolet seem to be rooted in the regions of magnetic low latitude, no sunspots, and draw the magnetic field lines open closed overlapping arches that connect the solar pole. Just emerge new flows of magnetic field in the vicinity of the increased activity, the filamentary structures are broken, “said Anik De Groof, a scientist working at the European Space Agency and who led the latest analysis of these observations. “The fact that these structures appear especially in the northern hemisphere could be related to an unusual inversion of the magnetic field polar occurred in cycle 24. However, in order to come to a solid conclusion will require further data and analysis from both SWAP that measures magnetic field.
Whatever the clues that will provide the new observations on the evolution of solar activity, for scientists will raise as many questions as they answer, and the new questions it hopes to answer with the future space missions dedicated to the sun. The mission sister PROBA2 called PROBA3 will keep the innermost region of the solar corona in white light with two space probes traveling in formation to create artificial eclipse. The Solar Orbiter, in the meantime, let the whole earth orbit, will move toward the ecliptic latitudes solar highest to observe the Sun’s poles by a distance less than the orbit of Mercury. These observations allow us to reveal the magnetic structure of the region where SWAP saw anchor many of the structures in a fan.

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