Scientists trace solar storms
For the first time, an international group of European, Americanand Indian researchers managed to
“Probing the heating of the Sun’s active region loops can helpus to better understand the physical mechanisms for more energeticevents which can impinge on the Earth’s environment,” co-authorHelen Mason from University of Cambridge commented.
Press release University of Cambridge
“The study published today by University of Cambridge scientistsworking with colleagues in India and the USA is the first tovisualise the movement of gases at one million degrees in coronalloops – solar structures that are rooted at both ends and extendout from active regions of the Sun. Active regions are the ‘cradle’for explosive energy releases such as solar flares and coronal massejections (CMEs).
The observation will help scientists understand what isconsidered to be one of the most challenging issues in astrophysics- how solar structures are heated and maintained in the upper solaratmosphere. Extreme solar activity can lead to severe space stormsthat interfere with satellite communications and damage electricpower transmission grids on Earth. Solar activity is cyclical, withthe next maximum forecast to occur around May 2013, and severespace weather is now listed very high on the UK’s 2012 NationalRisk Register of Civil Emergencies.
Unique observations
Based on observations from the Hinode satellite (a jointJapanese, NASA, European Space Agency and UK project), the newfindings provide the first evidence of plasma upflows travelling ataround 20 km per second in the one million degree active regionloops. The scientists suggest that the upflow of gases is probablythe result of “impulsive heating” close to the footpoint regions ofthe loops.
“Active regions are now occurring frequently across the Sun. Wehave a really great opportunity to study them with solarspacecraft, such as Hinode and the Solar Dynamics Observatory(SDO),” said co-author Dr Helen Mason from the University ofCambridge’s Department of Applied Mathematics and TheoreticalPhysics. “Probing the heating of the Sun’s active region loops canhelp us to better understand the physical mechanisms for moreenergetic events which can impinge on the Earth’s environment.”
Fingerprints of plasma flows
Previous ultraviolet images of the Sun taken by NASA’s SDO haveshown large loops of hot gas guided by the Sun’s magnetic field androoted near sunspots. Despite such remarkable developments in theobservations and theory of active regions over the past fewdecades, the question remained as to how solar plasma is heated andrises up into the loops in the first place.
Now, the new research provides the first visualisation of plasmaflow by showing the movement of gases within the loop as’blueshifts’ in diagnostic images using the extreme ultravioletimaging spectrometer (EIS) on the Hinode satellite. Spectral linesproduced by the spectrometer act like ‘fingerprints’ or the ‘barcode’ in a supermarket – the lines identify the multitude ofelements and ions within the loop and shifts in the position of thelines provide information on the motion of the plasma. Although theSun is composed mainly of hydrogen and helium, there are also othertrace elements, such as oxygen and iron, in the hot ionised gaswithin the loops.
The scientists suggest that the gas movement is caused by aprocess of “chromospheric evaporation” in which “impulsive heating”on a small scale can result in the heating of the solar activeregions but on a larger scale can lead to huge explosions, such assolar flares or coronal mass ejections.
Improving forecasting mechanisms
“It is believed that magnetic energy builds up in an activeregion as the magnetic field becomes distorted, for example bymotions below the surface of the Sun dragging the magnetic fieldsaround,” explained Mason, whose research is partially funded by theUK’s Science and Technology Facilities Council (STFC). “Sometimesmagnetic flux can emerge or submerge and affect the overlyingmagnetic field. We believe that solar plasma surges upwards whenimpulsive heating results from magnetic reconnection which occurseither in the loops or close to the Sun’s surface. Thesedisruptions are sometimes relatively gentle but can also becatastrophic.”
Commenting on the newly published study, Professor RichardHarrison MBE, Head of Space Physics and Chief Scientist at the STFCRutherford Appleton Laboratory, said: “The Sun governs theenvironment in which we live and it is the so-called solar activeregions that drive extreme conditions leading to the explosiveflares and the huge eruptions; understanding these active regionsis absolutely critical for the study of what we now call spaceweather. The work published by in this paper is a key element ofthat work, applying innovative analyses to the observations fromthe UK-led Hinode/EIS instrument.”
The researchers hope that a better understanding of activeregions might one day help scientists to identify the magneticfield structures that lead to explosive solar energy releases anduse this as a means for predicting when such events willoccur.”
