Microwave diagnostics of magnetic field strengths in solar flaring loops
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https://doi.org/10.1007/s11431-020-1620-7
Microwave diagnostics of magnetic field strengths in solar flaring loops ZHU Rui1, TAN BaoLin2,3, SU YingNa4,5, TIAN Hui1,2* , XU Yu6, CHEN XingYao2, SONG YongLiang2 & TAN GuangYu1 1 School of Earth and Space Sciences, Peking University, Beijing 100871, China; Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; 3 School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China; 4 Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China; 5 School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China; 6 School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China 2 Key
Received February 20, 2020; accepted May 6, 2020; published online August 26, 2020
We have performed microwave diagnostics of the magnetic field strengths in solar flaring loops based on the theory of gyrosynchrotron emission. From Nobeyama Radioheliograph observations of three flare events at 17 and 34 GHz, we obtained the degree of circular polarization and the spectral index of microwave flux density, which were then used to map the magnetic field strengths in post-flare loops. Our results show that the magnetic field strength typically decreases from ∼800 G near the loop footpoints to ∼100 G at a height of 10–25 Mm. Comparison of our results with magnetic field modeling using a flux rope insertion method is also discussed. Our study demonstrates the potential of microwave imaging observations, even at only two frequencies, in diagnosing the coronal magnetic field of flaring regions. solar magnetic field, solar flare, microwave observation, gyrosynchrotron emission Citation:
Zhu R, Tan B L, Su Y N, et al. Microwave diagnostics of magnetic field strengths in solar flaring loops. Sci China Tech Sci, 2020, 63, https://doi.org/10.1007/s11431-020-1620-7
1 Introduction The ubiquitous magnetic field in the solar atmosphere plays a crucial role in various types of physical processes, from small-scale eruptions such as microflares and mini-filament eruptions to large-scale eruptions such as two-ribbon flares and coronal mass ejections (CMEs). All these solar activities are driven by the evolution of the magnetic field. Hence, measurements of the solar magnetic field are very important. However, only the photospheric magnetic field can be measured through the Zeeman effect on a daily basis. The coronal magnetic field has not been routinely measured up to now, due to the large broadening of coronal emission lines and *Corresponding author (email: [email protected])
small Zeeman splitting caused by the weaker field. Despite these difficulties, Lin et al. [1, 2] managed to measure the coronal magnetic field in active regions using the infrared coronal emission line Fe XIII 1074.7 nm. However, this method requires a long integration time (order of
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