Disclaimer: machine translated by DeepL which may contain errors.
~ Message from a graduate student~.
Magnetic Field "Tornadoes" Heat the Solar Corona
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| Hidetaka Kuniyoshi |
| Department of Earth and Planetary Science, 1st Year Doctoral Student |
| Birthplace Okinawa, Japan |
| High School Showa Pharmaceutical University High School |
| Faculty Department of Earth and Planetary Physics, Faculty of Science, The University of Tokyo |
The existence of a planetary atmosphere is one of the most important conditions for life. To determine whether a planet can sustain an atmosphere, it is necessary to estimate the X-ray and ultraviolet (XUV) radiation from the host star correctly. The temperature of the corona is more than a million degrees Celsius, which is several hundred times hotter than the stellar surface (photosphere). At first glance, this fact seems odd, since the Sun's heat source is the central (core) solar system. This is because the source of the Sun's heat is the nuclear fusion reaction occurring at its center (core), and the temperature should decrease as one moves away from the core. Therefore, understanding the coronal heating mechanism is essential to the study of the possibility of life. Among stars, solar coronal heating, which is the subject of my research, has been particularly active. This is because the Sun is the only star that can be observed in spatially resolved detail, whereas other stars can only be observed as points.
The solar atmosphere is strongly affected by the magnetic field because it is in a state called plasma, which is ionized gas. It has been observed that photospheric plasma has a thermal convective motion similar to that of hot water over a fire. It is believed that the magnetic energy generated by the interaction between this convective motion and the solar magnetic field propagates to the corona and leads to heating, but the details of the energy transport system have not been well understood. However, recent advances in observational techniques have led to the discovery of the existence of an energy transport system called a magnetic tornado, which is driven by the ubiquity of small vortices generated by convection in the photosphere. A magnetic tornado is a phenomenon in which a vortex located at the foot of the solar magnetic field twists the magnetic field so that it penetrates from the photosphere to the corona, propagating energy with the generation of a tornado-like plasma flow. The reason for the efficient transport of energy has not been well understood as an issue in the study of magnetic tornadoes. Therefore, I am currently trying to elucidate the above mechanism by reproducing the magnetotornado generation in the solar atmosphere using a supercomputer and analyzing the three-dimensional structure in detail, which cannot be obtained only from observational data. As a result, I have discovered that magnetic tornadoes suppress energy dissipation before the corona arrives, resulting in efficient energy transport to the corona. However, there is still much to be clarified. For example, whether magnetic tornadoes are the dominant energy transport system everywhere in the Sun, and the mechanism by which the magnetic energy carried by the tornadoes to the corona is converted into heat are just a few examples.
(a) Magnetic field distribution in the solar atmosphere (© H. Tsujimura) and a schematic of the solar interior and atmospheric structure. Heat generated in the core is transported to the photosphere by radiation and convection. In the atmosphere, the magnetic field causes heating, resulting in a corona temperature several hundred times hotter than the photosphere.
(b) Magnetic field lines during magnetic tornado generation. The foot is rooted in the photosphere, and a twisted magnetic field is formed so that it penetrates all the way to the corona.
My decision to become a solar physicist was the result of following my intuition. As I continued my research, fascinated by the beauty that I did not feel in other astronomical phenomena, I realized that the driving force behind my research was love. The time I spend immersed in my research, guided by love and not by profit and loss or common sense, is the time I feel the most creative and free. There are many people around the world who share the same love of the sun, and cooperation with them is indispensable in my research life. I feel that the low threshold for international activities is another attraction of the field.