Investigation of Type III Radio Bursts in Different Phases of Solar Flares

• Main Authors: Shao-Fu Hsieh, 謝劭甫
• Other Authors: Ya-Hui Yang
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/76wz7h

碩士 === 國立中央大學 === 太空科學研究所 === 107 === The purpose of this study is to investigate the difference of the characteristics of type III solar radio bursts in different phases of solar flares. We use the dynamic spectrum observed by Solar Broadband Radio Spectrometer (SBRS) in the frequency range of 2.6-3.8 GHz and the EUV image observed by Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA). Type III solar radio bursts are believed to be produced by the non-thermal electron beams propagating in solar corona and interplanetary. The high-frequency type III radio bursts are produced at the region of high plasma density close to solar surface. Moreover, type III radio bursts are often associated with solar flares. In this study, we analyze the characteristics of type III bursts (bandwidth, duration, drift rate, intensity, and polarization) observed by SBRS in the three stages of solar flares, i.e., the pre-flare, impulsive phase and gradual phase. Our results show that the pre-flare type III has a longer duration, wider bandwidth and weaker intensity than those in the impulsive and gradual phases. In particular, we analyze the temporal correlation between pre-flare type III bursts and EUV emissions at solar source regions. We estimate the Fe XVIII line formed at 7 MK using AIA 94 Å, 171 Å and 211 Å. Then, all EUV brightening is attributable to plasma at 7 MK, and related with more than half pre-flare type III. Thus, the pre-flare type III events imply the existence of small-scale energy release before flares.