太空環境中的兩個觀測難題： 前艏震波區域波擾動斜向傳播現象與 接觸不連續面的存在證據

Two Long-standing Problems in Observation: Oblique Propagation of Foreshock ULF Wave and Existence of Contact Discontinuity

謝文傑(WEN-CHIEH HSIEH)

指導教授 ： 許志浤

國立中央大學/地球科學學院/太空科學研究所/博士(2015年)

摘要

在太空觀測研究的歷程中，有兩個爭論超過20個年頭的議題：徑向行星際磁場環境下前艏震波區域的波擾動斜向傳播現象，與自然環境中接觸不連續面的存在證據。在本論文中，我們使用 THEMIS 衛星任務資料來檢驗太陽風參數和斜向傳播現象之間的關係；我們同時從波動折射機制的觀點出發，得出一斜向傳播角度和太陽風參數的關係方程式。觀測結果和理論方程式皆顯示斜向傳播角度與波擾動的頻率和極性、行星際磁場強度以及太陽風速率無直接關係；而與太陽風速率和上、下游波擾動相速率三者間的比值有關。在接觸不連續面存在證據的議題上，我們提出了一個根據磁流體躍遷條件使用單一衛星資料選取接觸不連續面事件的可行方案，我們呈現了兩個接觸不連續面事件，一個存在於太陽風中而另一個發現於地球磁層內。接觸不連續面的寬度估計為11.7和4.3個離子迴旋半徑。

關鍵字

前艏震波 ； 接觸不連續面 ； 超低頻波擾動 ； 磁流體力學

並列摘要

Two problems in observations have lasted for more two decades: the oblique propagation of foreshock ultra-low frequency (ULF) wave and the existence of contact discontinuity (CD) in nature. Using the THEMIS data, we examine the relation between oblique propagation angles and solar wind parameters. Meanwhile, we derive the oblique propagation angle as a function of the solar wind parameters from the aspect of wave refraction. Both of the examinations from the observed relation and the prediction from the derived function reveal the irrelevance of oblique propagation angle to the wave frequency, the wave polarization, the strength of magnetic field and the solar wind speed. The oblique propagation angle is shown to be a function of a ratio between solar wind speed, the upstream and downstream wave phase speeds. As to the argument of existence of CD, we propose a practical process to find CDs with single-satellite data based on MHD jump conditions. Two CD events are presented, one in the solar wind and the other one in the magnetosphere. The width of the transition of a CD may range from 11.7 and 4.3 ion gyroradii.

並列關鍵字

Foreshock ； Contact Dicontinuity ； ULF wave ； Magnetodynamics

參考文獻

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[3] Balogh, A., et al. (2005), Cluster at the bow shock: Introduction, Space Sci. Rev., 118, 155–160, doi:10.1007/s11214-005-3826-1

[5] Billingham, L., S. J. Schwartz, and D. G. Sibeck (2008), The statistics of foreshock cavities: Results of a Cluster survey, Ann. Geophys., 26, 3653–3667, doi:10.5194/angeo-26-3653-2008.

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