| 摘要: | 太陽無線電波觀測，讓人們可以藉由遙測的方式，推測太陽日冕與行星際空間的背景狀態，亦或是太陽暫態活動的情形。本論文主要使用Parker Solar Probe (PSP) 於軌道1至軌道13期間 (2018年至2022年) 10.5 kHz至19.2 MHz的無線電波觀測資料，探討在內太陽圈環境觀測下，具有偏振表現的行星際三型太陽無線電波爆 (Interplanetary Type III solar radio burst) 訊號特性，並針對2020年01月27日與09月13日總共兩起三型無線電波爆事件，結合Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA) 的EUV影像與Solar Terrestrial Relations Observatory (STEREO) 和Wind衛星的無線電波觀測，分析三型無線電波爆的潛在源區。此外，本論文也針對2022年09月05日的複雜型三型無線電波爆 (Complex type III burst) 與2021年至2022年總共七起三型無線電波風暴 (Type III storm) 進行探討。
本論文研究分析太陽三型無線電波爆的特性包括：總強度訊號與偏振訊號的上/下截止頻率、頻率漂移率、偏振度、衰減時長。結果顯示偏振訊號的上截止頻率與總強度訊號上截止頻率統計分佈接近，但下截止頻率的部分，偏振訊號普遍高於總強度訊號；頻率漂移率的頻譜指數略大於過去觀測結果；右旋圓形偏振 (Right-hand circular polarization, RHC) 事件數多於左旋圓形偏振事件數 (Left-hand circular polarization, LHC)，最大偏振度介於0.4至1之間。另外，本論文研究所分析的偏振訊號主要有兩種型態，進一步針對軌道1至軌道8的該兩類型事件進行SEA分析 (Superposed epoch analysis)，顯示此兩種型態的特徵分別為：總強度峰值之後、指數衰減至背景之前無圓形偏振訊號；與總強度峰值之後仍具有一定的強度，並隨著頻率降低、持續時間有增長的類型。另外，總強度訊號的衰減時長在不同高低的頻率範圍與不同偏振型態的訊號中，隨頻率的變化情形略有差異。
而在個案分析結果中，本論文所探討的三型無線電波爆潛在源區皆是由太陽表面上之小型噴發事件造成的。針對複雜型三型無線電波爆事件的部分，偏振訊號只出現於下截止頻率附近，與大多數三型無線電波爆的偏振訊號形式不同。此外，在多方比對日冕儀影像後，確認所分析的複雜型三型無線電波爆是由Far-side的日冕物質拋射事件造成。最後，關於三型無線電波風暴的分析，顯示風暴期間的訊號皆具有明顯的偏振表現，LHC與RHC偏振表現事件數各占分析事件數總體一半，大部分具有頻率漂移的情形。;Solar radio emission provides a remote sensing probe for the solar corona, interplanetary space, and the solar transient activity. In this study, we analyze the interplanetary type III solar radio burst with circular polarization in the inner heliosphere observed by Parker Solar Probe (PSP) from 10.5 kHz to 19.2 MHz during its first thirteen orbits (2018-2022). We also examine two polarized type III events on 27 January 2020 and 13 September 2020 to find their potential radio source from radio observations observed by Solar Terrestrial Relations Observatory (STEREO), Wind, and EUV images observed by Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA). Besides, we investigate case studies of complex type III burst on 05 September 2022 and seven Type III storm events between 2021 and 2022.
There are four properties of interplanetary type III solar radio burst we analyzed: high/low cut-off frequencies, frequency drift rate, circular polarization, and decay time. The results indicate that the high cut-off frequency of the polarized signal is close to the high cut-off frequency of the total intensity, but the lower cut-off frequency of the polarized signal is generally higher than the lower cut-off frequency of the total intensity. The spectral index of the frequency drift rate is slightly larger than that of the past observations. The number of right-hand circular polarization (RHC) events is higher than that of left-hand circular polarization (LHC) events; the maximum polarization is between 0.4 and 1. We apply the SEA analysis (Superposed Epoch Analysis) for the polarized Type III events from Orbit 1 to Orbit 8. There are two types of polarized patterns examined: one is non-circular polarized signal after the maximum total intensity, the other is the longer lasting polarized signal with decreasing frequency. For decay time, it has a slightly different tendency of frequency in different frequency ranges and different patterns of polarized signal.
In the case studies, the potential radio sources of two polarized type III events studied in this paper are all caused by small eruptions on the solar surface. For the complex type III radio burst events, the polarized signal appears only near the lower cut-off frequency, which is very different from most type III radio bursts. After comparing the coronagraph images, it is confirmed that the complex type III radio burst was caused by Far-side coronal mass ejection (CME) event. For the results of type III storms, the number of analyzed LHC and RHC storms are close to each other. Furthermore, our findings suggest that the signals within storms have obvious polarization and most of them have frequency drift. |
