Consortium studies physics of solar flares
September 09, 2015
By Elton Alisson
Agência FAPESP – A consortium of seven European universities and research institutions has spent the past two years studying the physics of solar flares, considered the most intense energy bursts in the solar system.
The project is called F-CHROMA, short for Flare Chromospheres: Observations, Models and Archives. It is funded by the European Commission under the EU’s Seventh Framework Program (FP7) for research and technological development.
The only Brazilian involved is Paulo Simões, a postdoctoral researcher at the University of Glasgow’s School of Physics & Astronomy in Scotland.
Simões received scholarships from FAPESP for scientific initiation and postdoctoral research at Mackenzie Presbyterian University (UPM) in São Paulo, Brazil, as well as masters and PhD research at the National Space Research Institute (INPE).
Simões was invited by UPM’s Radio Astronomy & Astrophysics Center (CRAAM) to take part in a colloquium held in São Paulo in early August to discuss solar flares in the chromosphere.
“The main aim of the F-CHROMA project is to increase knowledge about the physics of solar flares by comparing current theories and models with observations at very high resolutions,” Simões told Agência FAPESP.
Solar flares are sudden eruptions on the sun’s surface characterized by the release of huge amounts of radiation. They may be caused by localized changes in the sun’s electromagnetic field. These events influence space weather and may disrupt human activities, including data transmission by satellites, for example.
Within a few minutes, a mid-sized solar flare can release an amount of energy equivalent to 100 million megatons of TNT, which is 10,000 times the energy stored in the world’s entire stockpile of nuclear weapons. Most of this energy is ultimately converted into electromagnetic radiation emitted mainly in the chromosphere. A thin, low-density layer of the sun’s atmosphere, the chromosphere, is located above the photosphere, the sun’s innermost layer, and below the corona, its outermost layer. Scientists now believe most of the electromagnetic radiation emitted by the sun dissipates in the chromosphere.
“Current theory suggests that electrons are accelerated in some part of the corona and cross the sun’s magnetic field to the chromosphere,” Simões said.
“On arrival in the chromosphere, the electrons collide with other particles that are already there, such as protons and other electrons, and deposit energy, altering the conditions in the chromosphere.”
The researchers’ goal is to understand how the chromosphere responds to this inrush of energy during a solar flare, in terms of changes in temperature and density, as well as ionization of elements such as hydrogen and helium.
“We’re interested in deepening our grasp of how solar flares begin and how they evolve. We also want to know what happens in the chromosphere as energy builds up and electromagnetic radiation rushes out,” Simões said.
“Last but not least, we aim to increase our knowledge of how solar flare energy is stored, released and converted into other forms.”
According to Simões, as with 99% of the visible universe, the sun’s atmosphere is made up of plasma (electrified gas), whose electrically charged ions and electrons produce a magnetic field.
By studying the release of energy and radiation in solar flares, he explained, researchers can achieve a better understanding of astrophysical plasma and the high-energy processes associated with various astrophysical objects, such as quasars.
“The sun is a plasma laboratory. By studying the sun, we can find out more about how this plasma and the sun’s magnetic field behave and how energy is transferred from one region to another, among many other matters,” Simões said.
Knowledge of the sun’s activity can also be applied to study other astronomical objects, such as stars, and can contribute to the search for habitable exoplanets (planets orbiting stars in other solar systems).
Flares are also observed on other stars, with more intensity than the flares seen on our own sun, but according to Simões scientists do not yet know why they occur.
“Most aspects of the physics of solar flares can be used to study other astronomical objects,” he said.
To study solar flares, the researchers who are participating in F-CHROMA combine data from satellite and ground-based observations with theoretical and advanced computational modeling.
Some of the ground-based solar observation is performed using optical telescopes, such as the Dunn Solar Telescope (DST) in New Mexico (USA) and the Swedish 1-meter Solar Telescope (SST) in the Canary Islands (Spain).
Space observation is performed using unmanned probes, such as the Solar Dynamics Observatory (SDO), launched in early 2010, and the Interface Region Imaging Spectrograph (IRIS), launched in June 2013. Both are missions of the US National Aeronautics & Space Administration (NASA).
Using data collected by the Atmospheric Imaging Assembly (AIA), an instrument on board the SDO that continuously observes the sun’s corona and the ultraviolet region of the chromosphere, and by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), another NASA mission, Simões and other researchers involved in F-CHROMA observed that at the onset of a solar flare the plasma in a region between the lower corona and the top of the chromosphere rises to very high temperatures, ranging between 6 and 12 million degrees.
“This had already been hypothesized by researchers in the early 1990s, but the observational data was insufficient to prove it,” Simões said. “We’ve now shown that the plasma in this region does indeed become extremely hot at the start of a solar flare.”
Findings from F-CHROMA will be used in the future to develop major solar observation projects, such as Hawaii’s Daniel K. Inouye Solar Telescope, expected to see first light in 2019, and the European Space Agency’s Solar Orbiter, scheduled for launching in 2018 and set to be one of the first probes to reach the vicinity of the sun.
The article “Impulsive heating of solar flare ribbons above 10 MK” (doi: 10.1007/s11207-015-0709-9) by Simões et al. can be read in the journal Solar Physics at link.springer.com/article/10.1007%2Fs11207-015-0709-9#.
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