The study, which was led by Dr. Chen, is reported in Issue 52 of Science in China (G) because of its significant research value.
Many explosive phenomena on the Sun, such as solar flares, involve the energy conversion from the magnetic energy to thermal and kinetic energies in the corona, which is the outer atmosphere of the Sun. Therefore, the coronal magnetic field is extremely crucial in the understanding of these eruptive phenomena.
However, at present, only the magnetic field along the solar surface can be measured directly, whereas the magnetic field in the solar corona can hardly be measured. Despite some efforts of measuring through infrared spectral lines and of the inversion through radio emissions, the coronal magnetic field is generally approximated by extrapolating the magnetic field from the solar surface, which is however an ill-posed problem. Therefore, it would be great to have an alternative approach to diagnose the coronal magnetic field.
In 1997, the EUV Imaging Telescope (EIT in short) on board the European–US satellite, Solar and Heliospheric Observatory (SOHO), discovered an unexpected wavelike phenomenon propagating in the solar corona, which was later named "EIT waves" after the telescope. "EIT waves" were explained successfully to be apparently propagating density enhancements compressed by the successive stretching of magnetic field lines during coronal mass ejections (CMEs), the largest-scale eruptive phenomenon on the Sun.
According to this model, the "EIT waves" propagation velocity is intimately determined by the 3-dimensional distribution of the coronal magnetic field. Based on such an interesting property, Dr. Chen proposed recently that the profile of the "EIT wave" propagation velocity can be utilized to probe the coronal magnetic field.
Dr. Chen told the reporter: "You know, we can already diagnose the deep structure of the Earth by analyzing seismic waves. Similarly, we now can diagnose the magnetic field in the solar corona by analyzing EIT waves, which in some sense can be analogized as helioseismic waves." He commented that, in this sense, "EIT wave" observations open a new window for solar physicists to look into the mysterious magnetic field in the solar corona, and would help uncover the explosive nature of many explosive phenomena, including solar flares. As also commented by a reviewer, "This is an interesting paper describing the observations and modeling of EIT waves, and illustrating how they can be applied to probe the global magnetic field in the corona".
"EIT waves" were originally explained as the magnetoacoustic waves, i.e., sound waves coupled with the magnetic field. Such a model was also used to estimate the magnetic field in the low corona. However, the magnetoacoustic wave model cannot account for various characteristics of "EIT waves". To reconcile the discrepancies, Dr. Chen and his collaborators from China, USA, and Japan put forward the magnetic field-line stretching model since 2002, which has been widely recognized in the solar physics community. In this newly published paper, Dr. Chen demonstrated that it is feasible to diagnose the magnetic field in the solar corona using the observations of "EIT wave" velocity profiles.
With the application of the "EIT wave" diagnostics, the 3-dimensional distribution of the solar coronal magnetic field is expected to be revealed, which would finally help unveil the nature of solar flares and CMEs, the two major driving sources of hazardous space disturbances to human high-tech activities, including navigations, telecommunications, manned missions, etc.
Dr. P. F. Chen is working in Department of Astronomy, Nanjing University. The department is one of the lead groups of astronomy research in China. The research was sponsored by National Natural Science Foundation of China (Nos. 10403003 and 10673004) and the Key Project of Chinese National Programs for Fundamental Research and Development (2006CB806302).
References:1. Chen P F. EIT waves and coronal magnetic field diagnosis. Sci China G-Phys Mech Astron, 2009, 52(11): 1785-1789
http://springer.r.delivery.net/r/r?2.1.Ee.2Tp.1hW1Qv.ByxLWW..H.Ixxu.3Geu.bW89MQ%5f%5fDUSeFVZ02. Chen P F, Wu S T, Shibata K and Fang C. Evidence of EIT and Moreton waves in numerical simulations. Astrophys J, 2002, 572: L99-L102
http://www.iop.org/EJ/abstract/1538-4357/572/1/L99/3 Chen P F, Fang C and Shibata K. A full view of EIT waves. Astrophys J, 2005, 622: 1202-1210
P. F. Chen | EurekAlert!
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
16.07.2018 | Chinese Academy of Sciences Headquarters
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
16.07.2018 | Physics and Astronomy
16.07.2018 | Life Sciences
16.07.2018 | Earth Sciences