Skip to main content

Radiophysics of the Sun

Final Report Summary - RADIOSUN (Radiophysics of the Sun)

More than 90% of the visible Universe is in the form of a plasma – the fourth state of matter. The study of the physical properties of plasma forms one of the most far ranging and challenging research areas in physics today. From cosmological objects to controlled fusion, this complex, but fundamental state of matter is proving to be of ever-greater significance in understanding the dynamics of the Universe and in harnessing the material world for the greatest technological result and the improvement of our society.

The strategic aims of plasma research are connected with the global challenges faced by humankind. One is the ecologically friendly and practically endless source of energy, the controlled fusion reaction that is believed to be achievable in magnetic confinement reactors, tokamaks with plasma being the working body. Another is the understanding of the key ingredient of the Earth’s climate change, the solar radiation. Also, the plasma research plays the central role in Space Weather, the study of the solar-terrestrial relations through the physical processes operating in the heliosphere. This branch of science is becoming increasingly important in the context of space exploration, e.g. Moon and Mars expeditions, and the stability and safety of space-based telecommunication and tele-navigation systems, energy supply lines and pipelines. Last but not least is the study of plasma physics of fundamental astrophysical processes. This makes the plasma research one of the strategic directions of Physical Sciences.

Despite of the abundance of the plasma state of matter in the Universe, the physical conditions on the Earth do not allow us to reach the plasma easily. The intrinsic difficulties of the laboratory plasma research are the cost and the technological problems of plasma creation and confinement. This motivates our interest in the space plasma systems, such as the corona of the Sun, the upper, fully-ionised and very hot part of the solar atmosphere, which is a natural plasma laboratory that provide us with a vast variety of plasma configurations and physical conditions.

One of the key observational windows provided by the Earth’s atmosphere is the high-frequency part of the radio band, from about 10 MHz to THz. This is a particularly important range of frequencies for the diagnostics of the solar atmosphere. The importance and wide interest to solar radiophysics research is brightly evident from the width and the spread of the international efforts towards developing solar radio-observational facilities, including the Chinese Spectral Radioheliograph (CSRH), the upgrade of the Siberian Solar Radio-telescope (SSRT) the Atacama Large Millimeter Array (ALMA), and the LOw Frequency Array (LOFAR). These advanced observational facilities are to revolutionise our understanding of basic plasma processes operating on the Sun, solar-terrestrial relations and Space Weather forecasting.

The aims of this project were to establish close research interaction and collaboration between the key research groups involved in CSRH, SSRT and ALMA projects and in development of relevant theory and data analysis tools, through the systematic research staff and knowledge exchange and joint research efforts exploiting existing data and facilities, and preparing the future world-class partnership in exploitation of the upcoming facilities. All these aims were fully accomplished.

The network consisted of 7 internationally recognised and respected research teams, the Astronomical Institute of Czech Republic, Glasgow University, UK, University of Maria Skladowska Curie, Poland, University of Warwick, UK, National Astronomical Observatory of China, and Institute for Solar-Terrestrial Physics and Pulkovo Observatory, Russia, with high level of expertise in the fields that are complimentary and crucial for the proposed research: solar radio instrumentation, data analysis, plasma physics of the microwave emission, magnetohydrodynamic (MHD) theory and simulations, and leadership or direct involvement in the upcoming CSRH, SSRT and ALMA facilities.

Addressing the specific objectives of the project, we significantly advanced our understanding of basic physical processes operating in solar flares, including the demonstration that quasi-periodic pulsations are a common feature of flares, which allowed us to develop and apply the novel method of combined microwave-MHD diagnostics of coronal plasma. We revealed the mechanisms for chromospheric-coronal connectivity by MHD waves. We develop strategies for the detection of chromospheric waves in mm and sub-mm with ALMA. We designed the novel data analysis tools, such as the Empirical Mode Decomposition and Pixelised Wavelet Filtering, and implemented them for the analysis of wave patterns in SDO/AIA, NoRH and SSRTdata sets, and developed a web-based interactive system for the analysis of imaging datacubes. We reached major progress in our understanding of the physical mechanisms responsible for the generation of the enigmatic sub-THz emission in flares. The project participants provided a major contribution and leadership to the SSALMONetwork that aims at co-ordinating the further development of solar observing modes for ALMA.

Seconded visits and five workshops and summer schools run by our network in Beijing, Lublin, Pulkovo, Irkutsk and Ondrejov, provided early-career researchers with extensive training in fundamental physics and crucial practical skills, such as the physics of the solar flares, flare radio-emission, theory of nonlinear dynamical systems, MHD wave theory, physics of the solar atmosphere, analysis of wave processes, numerical modelling of MHD processes, modern data analysis techniques, and foundations of radio-interferometry, as well as an excellent environment for practising the presentation skills. The project contributed to 16 successful PhD theses. Additional information about the project activities could be found on the web-site

Our research results have been published in 49 research papers in leading international scientific journals, such as the Astrophysical Journal, Astronomy & Astrophysics, Advances in Space Research, and Solar Physics, and a dedicated special issue was published in Research in Astronomy and Astrophysics, and became subject to a number of contributed talks, poster presentations, invited reviews and plenary lectures at several major international conferences, such as the European Solar Physics Meeting, Ireland, European Week of Astronomy and Astrophysics, Spain; International Congress on Plasma Physics, Taiwan, Asian-Pacific Solar Physics Meetings in Hangzhou and Seoul, COSPAR General Assembly, Moscow, and many others. The activity created a solid foundation for the foundation of the Solar and Heliospheric Working Group in the Square Kilometre Array (SKA) project. Also, the project resulted in the application for an H-2020 European Cooperation in Science and Technology funding with the proposal “Solar Radio Astronomy Network”.