For the first time, an international group of European, American
and Indian researchers managed to
observe Sun gases surging into coronal loops. This way,
scientists hope to get a better understanding of the mechanisms
behind solar storms which can have a severe impact on communication
satellites and power grids.
"Probing the heating of the Sun's active region loops can help
us to better understand the physical mechanisms for more energetic
events which can impinge on the Earth's environment," co-author
Helen Mason from University of Cambridge commented.
Press release University of Cambridge
"The study published today by University of Cambridge scientists
working with colleagues in India and the USA is the first to
visualise the movement of gases at one million degrees in coronal
loops - solar structures that are rooted at both ends and extend
out from active regions of the Sun. Active regions are the 'cradle'
for explosive energy releases such as solar flares and coronal mass
ejections (CMEs).
The observation will help scientists understand what is
considered to be one of the most challenging issues in astrophysics
- how solar structures are heated and maintained in the upper solar
atmosphere. Extreme solar activity can lead to severe space storms
that interfere with satellite communications and damage electric
power transmission grids on Earth. Solar activity is cyclical, with
the next maximum forecast to occur around May 2013, and severe
space weather is now listed very high on the UK's 2012 National
Risk Register of Civil Emergencies.
Unique observations
Based on observations from the Hinode satellite (a joint
Japanese, NASA, European Space Agency and UK project), the new
findings provide the first evidence of plasma upflows travelling at
around 20 km per second in the one million degree active region
loops. The scientists suggest that the upflow of gases is probably
the result of "impulsive heating" close to the footpoint regions of
the loops.
"Active regions are now occurring frequently across the Sun. We
have a really great opportunity to study them with solar
spacecraft, such as Hinode and the Solar Dynamics Observatory
(SDO)," said co-author Dr Helen Mason from the University of
Cambridge's Department of Applied Mathematics and Theoretical
Physics. "Probing the heating of the Sun's active region loops can
help us to better understand the physical mechanisms for more
energetic events which can impinge on the Earth's environment."
Fingerprints of plasma flows
Previous ultraviolet images of the Sun taken by NASA's SDO have
shown large loops of hot gas guided by the Sun's magnetic field and
rooted near sunspots. Despite such remarkable developments in the
observations and theory of active regions over the past few
decades, the question remained as to how solar plasma is heated and
rises up into the loops in the first place.
Now, the new research provides the first visualisation of plasma
flow by showing the movement of gases within the loop as
'blueshifts' in diagnostic images using the extreme ultraviolet
imaging spectrometer (EIS) on the Hinode satellite. Spectral lines
produced by the spectrometer act like 'fingerprints' or the 'bar
code' in a supermarket - the lines identify the multitude of
elements and ions within the loop and shifts in the position of the
lines provide information on the motion of the plasma. Although the
Sun is composed mainly of hydrogen and helium, there are also other
trace elements, such as oxygen and iron, in the hot ionised gas
within the loops.
The scientists suggest that the gas movement is caused by a
process of "chromospheric evaporation" in which "impulsive heating"
on a small scale can result in the heating of the solar active
regions but on a larger scale can lead to huge explosions, such as
solar flares or coronal mass ejections.
Improving forecasting mechanisms
"It is believed that magnetic energy builds up in an active
region as the magnetic field becomes distorted, for example by
motions below the surface of the Sun dragging the magnetic fields
around," explained Mason, whose research is partially funded by the
UK's Science and Technology Facilities Council (STFC). "Sometimes
magnetic flux can emerge or submerge and affect the overlying
magnetic field. We believe that solar plasma surges upwards when
impulsive heating results from magnetic reconnection which occurs
either in the loops or close to the Sun's surface. These
disruptions are sometimes relatively gentle but can also be
catastrophic."
Commenting on the newly published study, Professor Richard
Harrison MBE, Head of Space Physics and Chief Scientist at the STFC
Rutherford Appleton Laboratory, said: "The Sun governs the
environment in which we live and it is the so-called solar active
regions that drive extreme conditions leading to the explosive
flares and the huge eruptions; understanding these active regions
is absolutely critical for the study of what we now call space
weather. The work published by in this paper is a key element of
that work, applying innovative analyses to the observations from
the UK-led Hinode/EIS instrument."
The researchers hope that a better understanding of active
regions might one day help scientists to identify the magnetic
field structures that lead to explosive solar energy releases and
use this as a means for predicting when such events will
occur."