Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Radio bursts are ubiquitous in the cosmic plasma. Solar radio emission mainly comes from the outer atmosphere of the sun. It is an induced radiation phenomenon generated by the interaction between energetic electrons and solar atmospheric plasma. Different dynamic spectra of solar radio bursts (SRBs) contain physical information of the plasma structure and state in the radiation source region. Therefore, the radiative mechanism of radio bursts has always been the object of research. There are two kinds of coherent radiation mechanisms related to solar radio bursts: one is the plasma radiation mechanism based on electron Langmuir frequency; the other is the electron cyclotron maser (ECM) radiation mechanism based on the electron cyclotron frequency. Although these two radiation mechanisms were proposed almost at the same time, based on the understanding of the coronal environment and the ECM mechanism at that time, the ECM radiation mechanism did encounter some difficulties in explaining SRBs. Until 1979, Wu $\&$ Lee introduced the relativistic effect and used the ECM radiation to explain the earth's Auroral Kilometric Radiation (AKR). Since then, the ECM emission has attracted wide attention. Considering some difficulties in applying the ECM emission mechanism to SRBs, we proposed a series of modified models in recent years. Firstly, the cutoff in the energy spectrum of the power-law electrons can effectively drive the ECM instability without relying on the anisotropic distribution of electron velocity. Secondly, considering the influence of Alfv\'{e}n wave perturbations which are prevalent in space and celestial plasmas, a self-consistent ECM emission mechanism excited by energetic electron beams is developed. On this basis, this paper summarizes the application of the ECM emission mechanism in traditional SRB phenomena from type I to V and microwave SRBs in recent years.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： Electromagnetic Ion Cyclotron (EMIC) waves in the solar wind have received much attention since they were discovered. EMIC waves are important in the plasma heating and acceleration in the solar wind because they can effectively transfer wave energy to ions via the cyclotron resonance. This paper summarizes the progress of EMIC waves observation and theoretical research in the solar wind, including a series of results obtained from EMIC waves observation in and out of magnetic clouds, Interplanetary Coronal Mass Ejections (ICMEs) sheath region, and the research progress for excitation mechanism of EMIC waves based on observations. Finally, the potential research of EMIC waves in the solar wind in the future is anticipated.
Subjects: Astronomy submitted time 2023-07-14 Cooperative journals: 《天文学报》
Abstract： The solar wind originates from the solar atmosphere. It undergoes heating when it propagates in the interplanetary space. It is unclear what heats the solar wind, a frontier problem in space physics. The solar wind is commonly in the state of turbulence, and the turbulence energy is believed to be an important source of the solar wind heating. However, two key questions remain, i.e., what is the specific medium heating the solar wind and what is the microscopic mechanism of the heating. This paper reviews the history of the studies on the solar wind heating problem, with the focus on domestic works about solar wind ion-scale turbulence and its heating. This paper also raises several questions to be solved and interesting topics on the solar wind heating in the future.
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