在極冠地區的帶電粒子產生的游離效應;Ionization Aspects of Polar Cap Absorption Effect

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題名:	在極冠地區的帶電粒子產生的游離效應;Ionization Aspects of Polar Cap Absorption Effect
作者:	狄米奇
貢獻者:	太空科學研究所
關鍵詞:	大氣科學類
日期:	2009-07-01
上傳時間:	2010-06-21 10:56:15 (UTC+8)
出版者:	行政院國家科學委員會
摘要:	來自於太陽的高能電子、中高緯度電離層和大氣層，電子斷層掃瞄術（二）計畫英文摘要。（五百字以內）來自於太陽的高能電子(SEP)，穿過磁層，造成在電離層以及中高緯度上層大氣有豐富的電子游離。這些強烈的SEP事件的能量貢獻能夠與極光以及太陽來的電磁波幅射的游離效應不相上下。因此，SEP是太陽風-磁層-大氣層中的重要一環，SEP對於高緯度的電離層以及大氣層的影響，也就是所謂的polar cap absorption (PCA)效應，是我們感興趣的，這對於研究跨極區的無線電通訊有很好的應用。然而，我們對於所謂的PCA效應仍然不是很了解，主要的是因為我們對於造成PCA效應的SEP能譜不是很了解，SEP能譜在不同的事件非常不同，SEP穿過的極冠區邊界層(polar cap boundary)與能量有關，而且不同的時間、不同的太陽風與地磁情況而有所不同。此外， SEP穿過的極冠區邊界層是複雜的，由於半影作用。另外一個問題是我們對於電離層以及高層大氣空間上的不均勻以及隨時間的變化並不太清楚。衛星為PCA影響的研究打開新的機會，數個低軌道的繞極衛星，例如四個POES衛星, SAMPEX, CORONAS-F, Tatiana-1，提供直接測量SEP的機會，另外COSMIC/FORMOSAT-3太空任務包含六顆衛星，利用無線電掩星的方法也提供詳細測量電子密度(electron content, EC)隨高度的剖面圖，加上地面GPS的雷達站，提供我們絕佳的機會去研究電子密度的三維結構。根據新的實驗資料顯示，我們提出研究PCA的計劃。我們根據直接測量高能電子的強度與能譜，我們能夠計算電離層與大氣層的SEP造成的游離效應，比較測量的電子密度，可以讓我們重新計算SEP的模型，包含游離率、以及電子重合作用(recombination)與吸附作用(attachment)。我們可以透過數個衛星的觀測，去了解極冠區邊界層以及動力作用。極冠區邊界層的位置及形狀也可以用地磁與太陽風的參數去模擬，利用這種方法，我們可以建立PCA效應的半經驗模型。solar energetic particles, middle and high latitude ionosphere and atmosphere, electron content tomography （二）計畫英文摘要。（五百字以內） Solar energetic particles (SEP) penetrating to the magnetosphere cause abundant ionization of the ionosphere and upper atmosphere at middle and high latitudes. Energy contribution of strong SEP events can be comparable with the auroral precipitation because of hard spectra extending to very high energies. The SEP ionization in the bottom-side ionosphere and atmosphere can be also comparable with and even exceeds the ionizing effect of the solar electromagnetic radiation. Hence the SEP precipitation is an important part of the solar wind – magnetosphere – ionosphere – atmosphere chain. Despite of the long history of experimental and model studies, the SEP impact to the high-latitude ionosphere and atmosphere, so-called polar cap absorption (PCA) effect, is still a subject of great interest because of high practical importance of radio wave propagation for cross-polar air flights. However understanding of that effect is still far from complete due to several circumstances. The PCA effect depends directly on the SEP spectrum, which is very variable from event to event and within a one particular event. The boundary of SEP penetration is energy-dependent and varies widely with longitude, local time as well as with changing of solar wind and geomagnetic conditions. In addition, the boundary itself can be pretty thick and complex because of penumbra effect. Another problem is a poor knowledge of ionization spatial distribution in that region because of limited number of experimental facilities and high temporal variability of the high-latitude atmosphere and ionosphere. Last advantages in space exploration open new opportunities for studies the PCA effect. Several low-earth’s orbit (LEO) satellites with polar orbits, such as constellation of 4 POES satellites, SAMPEX, CORONAS-F, Tatiana-1 perform direct measurements of the precipitating SEP. New frontier is achieved by the COSMIC/FORMOSAT-3 space mission consisting in constellation of 6 satellites, which provide detail measurements of electron content (EC) height profiles by using radio occultation technique. Together with ground-based observations conducted by radars and receivers of radio signals from GPS and LEO satellite, the COSMIC/FORMOSAT-3 give us an unique opportunity to study a 3D distribution of the EC in the high- and mid-latitude ionosphere and upper atmosphere. Based on the new experimental data we propose a comprehensive study of PCA effect. The SEP ionization of ionosphere and atmosphere will be calculated on the base of direct measurements of the intensity and spectra of penetrating particles. Comparison of the calculated ionization with the observations permits improvement the model of SEP ionization by accounting the realistic rates of losses in recombination and attachment. The polar cap boundary and its dynamics will be determined from direct multi-satellite observations. The location and shape of the boundary will be modeled as a function of local time, geomagnetic and solar wind parameters. By this way a semi-empirical model of the PCA effect will be developed. 研究期間：9801 ~ 9807
關聯:	財團法人國家實驗研究院科技政策研究與資訊中心
顯示於類別:	[太空科學研究所 ] 研究計畫

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