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| 題名: | 日冕洞與開放磁場區的特性與差異以及長期觀測;Coronal Holes and Open Magnetic Field Regions: Properties, Differences and Long-term Behaviors |
| 作者: | 黃冠瀚;Huang, Guan-Han |
| 貢獻者: | 太空科學與工程研究所 |
| 關鍵詞: | 日冕洞;開放磁場區;coronal hole;open magnetic field region |
| 日期: | 2023-01-09 |
| 上傳時間: | 2024-09-19 14:47:54 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 日冕洞（coronal hole）是日冕持續且不斷發生的現象。他們是在太陽盤面上低亮度且由單一磁極主導的區域，或是磁場線延伸至行星際空間中的「開放」磁場（open magnetic field）區域。這兩種定義雖然具有關聯，但是卻不完全一樣。在此研究中，我們只把具有第一種性質的現象稱呼為日冕洞，並且量化日冕洞與開放磁場區的差異，接著研究造成此差異的來源;以及研究開放磁場區在長時間尺度下的演變。
我們根據太陽動力學天文台（SolarDynamicsObservatory）自卡靈頓週期（Carrington rotation number）2099至2227的極紫外光（extreme ultraviolet）資料與磁場資料，建立這兩種物理量的綜觀影像（synoptic map），並從中擷取出日冕洞;以及使用勢場（potential field）、無作用力場（force-free field）、熱磁流體（thermal magnetohydrodynamic）為基礎建立出開放磁場區;接著再比較日冕洞與開放磁場區的差異。我們也由熱磁流體的資料建立出日冕洞，與同為熱磁流體資料所建立的開放磁場區作比較，藉此來驗證我們的發現。
將日冕洞、開放磁場區與高速太陽風（high-speed solar wind stream）比較之後，我們發現開放磁場區比起日冕洞與高速太陽風更為相關;造成此差異的來源可分為亮度較高的開放磁場區，以及具有封閉磁場線的日冕洞兩種。分析結果指出：一、極紫外線的亮度與磁場線的擴張因子（expansion factor）在對數上有正相關，因此擴張因子較大的開放磁場區會有較高的亮度，而被判斷為非日冕洞區;二、日冕洞的封閉磁場線可以跨日冕洞與非日冕洞區或與其他日冕洞連接，因此對日冕洞的單一磁極也有貢獻;三、開放磁場區在長時間尺度會形成「極至極跨赤道（pole-to-pole trans-equatorial）」的遷移，並且遷移的速度與子午流（meridional flow）的速度相當。
本研究使用到的 EUV 與磁場綜觀影像、合成 EUV 影像、日冕洞、高速太陽風，皆發表於https://doi.org/10.34740/kaggle/ds/2783160。;Coronal holes are persistent and recurrent features in the solar corona. They are observationally defined as dark patches with predominantly unipolar magnetic field, or theoretically as regions with magnetic field lines extending far into the interplanetary space ("open" magnetic field regions). The two definitions, however, do not always coincide with each other. In this study, the first definition will be referred to as coronal hole (CH) and the second definition as open magnetic field (OMF) region. We aim to quantify the difference between the two physical phenomena, investigate the sources of inconsistencies between the two, and study the long-term evolution of the OMF regions.
The CHs are extracted from the synoptic maps constructed using the magnetic field and extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO). The time period of the synoptic maps spans from the Carrington Rotation (CR) number 2099 to CR2227. The extracted CHs are compared with the OMF regions constructed from potential field model, linear force-free model, and thermal magnetohydrodynamic (MHD) model. The OMF regions from the MHD model are also compared with the CHs extracted from the thermal MHD data for theoretical analysis.
By comparing the CHs and the OMF regions with the high-speed solar wind streams (HSSs), we found that the HSS source regions are more consistent with the OMF regions than with CHs. The inconsistency between the CHs and the OMF regions can come from two sources: OMF regions with high EUV intensities and CHs with closed magnetic field structures. Our analysis shows that (1) the EUV intensity is approximately positively correlated with the expansion factor of magnetic flux in logarithmic scale, which means that an OMF region with a sufficiently large expansion factor is likely to be bright in EUV images, and therefore not be qualified as a CH; (2) the closed magnetic field lines can cross the CH boundaries to connect with non-CH regions or with different CHs, thereby contributing a non-negligible amount of unipolarity to the CHs; (3) the long-term evolution of the OMF regions forms a pole-to-pole trans-equatorial migration pattern, and the speed of the migration is comparable to the measured meridional flow speed. The data used in this study, including the EUV and magnetic field synoptic maps, the synthetic EUV maps, the identified coronal holes, and the identified high-speed solar wind streams, are distributed on https://doi.org/10.34740/kaggle/ds/2783160. |
| 顯示於類別: | [太空科學研究所 ] 博碩士論文
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