多能量通道之極區沉降粒子研究;A Study on Auroral Precipitating Particles in Terms of Energy Channels

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Title:	多能量通道之極區沉降粒子研究;A Study on Auroral Precipitating Particles in Terms of Energy Channels
Authors:	沈涵文;Shen, Han-Wen
Contributors:	太空科學與工程研究所
Keywords:	極光;粒子沉降;地磁活動;行星際磁場;磁層-電離層耦合;電漿物理;Aurora;Particle precipitation;Geomagnetic activity;Interplanetary magnetic field;Magnetosphere-Ionosphere coupling;Plasma physics
Date:	2022-07-02
Issue Date:	2022-10-04 11:00:48 (UTC+8)
Publisher:	國立中央大學
Abstract:	極光是原子或分子與沉降粒子碰撞產生的現象，而沉降粒子則由磁層的一些物理機制導致。以往對極光物理的研究大多採用極光影像或在一個寬能量範圍內的沉降粒子之通量資料，而他們呈現的結果通常為不同能量的沉降粒子的綜合效應。與以往研究不同的是，我們採用四個相對較窄的能量通道之粒子通量資料來探索極光粒子沉降。本論文的第一個研究主題是探討地磁活動對整個極區沉降粒子通量空間分布的影響。研究結果顯示無論在地磁活躍或寧靜時期，低能(< 1 keV)和高能(1-10 keV)沉降粒子分別主要分布於日側和夜側。透過我們得到的空間分布與過去結果之比較，發現高能沉降電子在寧靜期主要是由於投擲角散射，而在活躍期主要是由準靜態電位結構加速和阿爾文加速產生。低能沉降電子在寧靜或活躍期則都主要由上述兩種加速機制產生。此研究結果還展示了夜側高能沉降質子以及電子根據地磁狀態而改變的晨昏不對稱分布。由於夜側磁層的梯度及曲率漂移效應，高能沉降質子和電子在寧靜期分別主要分布在午夜前和午夜後，而在磁尾的磁副暴相關物理過程會導致它們在活躍期的分布對調。本論文的第二個探討主題是行星際磁場的By分量之極性對日側極區沉降電子的影響。研究結果表明，688−1000 eV能量範圍內的電子通量反應與跨半球場向電流有關，而154−224 eV能量範圍內的通量反應與磁鞘電子通過反平行磁重聯進入有關。在這個主題中，我們還發現了可能自然存在的日側極區沉降電子之兩種半球不對稱性。總結來說，將沉降粒子根據能量通道分別探討提供了我們對極光物理了解的新的視角，這些結果也有助於我們了解磁層動力過程。;Aurora is a phenomenon generated by collisions of atoms with precipitating particles. These precipitating particles are created by physical mechanisms behind the dynamic magnetosphere. Previous studies on auroral physics usually utilized auroral images or fluxes over a substantial energy range of precipitating particles. However, their results are often manifested from combined effects of precipitating particles with different energies. Unlike past studies, we explored the auroral particle precipitation using particle data of four relatively narrow energy channels. The first topic of this study is effects of geomagnetic activity on the spatial distribution of precipitating particles in the whole polar ionosphere. It is found that, regardless of active and quiet times, low‐energy (< 1 keV) and high‐energy (1–10 keV) precipitating particles are mostly on the dayside and nightside, respectively. A comparison with past results reveals that high‐energy precipitating electrons are mostly due to pitch angle scattering during quiet times and are mainly produced by quasi‐static potential structures acceleration and Alfvénic acceleration during active times; while low‐energy ones are predominantly caused by the two acceleration mechanisms regardless of quiet and active times. Our results also demonstrate a dawn‐dusk asymmetric distribution of nightside high‐energy protons/electrons in reference to the geomagnetic state. High‐energy precipitating protons and electrons are respectively on premidnight and postmidnight during quiet times because of the curvature and gradient drifts of magnetospheric particles, but their distributions during active times are swapped due to substorm-related processes in the magnetotail. Our second topic is effects of the IMF By polarity on dayside precipitating electrons. The results demonstrate that the response in the energy range of 688–1000 eV is associated with interhemispheric field-aligned currents, and that the response in the energy range of 154–224 eV is related to the direct entry of magnetosheath electrons via antiparallel reconnection. In this topic, we also discovered two types of hemispheric asymmetry in the dayside electron precipitation that may be naturally preexisting. In summary, all the results derived from this study provide a new look at particle precipitation, which can help reveal the secret of the dynamic magnetosphere.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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