南大西洋磁場異常(SAA)區中心帶的地理位置約位在南緯10 至35 度之間而經度範圍則跨東經270 至330 度之間｡ 就同一高度而言，SAA 區的磁場強度遠弱於其它經緯度區域的磁場強度｡ 而通過SAA 區磁力線的遠點可高達輻射帶(范愛倫帶)高度，甚至於非常接近磁爆期之環電流位置｡ 由於此區的特殊磁場結構，能量高達數千乃至數十億電子伏特的帶電粒子可能深穿大氣層而將此區大氣層的中性氣體游離化或提升它們的能量｡但因穿入粒子能量的不同及接受能量之大氣成分隨高度有異，其交互作用所造成之電離層結構變化也會視高度而有所差別｡ 另方面在水平方向上也會因SAA 區電子密度之增加而造成與鄰區之密度梯度(或相當於導電度梯度)，此梯度可就地引發新的電場，而後此電場可驅動電離層電漿之再分佈，有時甚至促成有利於電漿不規則體發展的環境條件｡ 我們計畫將借重福三資料以探討這一連串電離層變化過程｡福衛三號星系自發射後不久即持續提供研究界利用無線電掩星技術所導出的電離層密度之高度變化資料，也提供由信號對雜訊比所推導的閃爍指標資料｡ 此外更提供了由地面接收福三的三頻段信標儀資料所推導出的電離層參數｡其中靠無線電掩星觀測所推導之高度變化鑑別度可小至一公里以內｡ 因為高能粒子比較容易深入SAA 大氣層，福衛二號上之觀測高空短暫發光現象酬載即選擇當飛越SAA 上空就關機的運作模式以避免高能粒子的迫壞｡許多放置在其他衛星上之儀器經過該區時也採取同樣運作模式｡ 幸運的是靠無線電掩星技術，福三星系可免受此限制而持續提供高垂直解析度電離層資料｡在本計畫執行期間我們將以福三資料為主，其他行星際或繞近地太空環境之衛星資料為輔，以研究磁爆期間高能粒子與電離層結構的藕合過程及它們型態變化的相關性｡ 相信本計畫的研究成果不但對研究磁層-電離層 -大氣層間的藕合現象有所助益，也會對飛越南大西洋磁場異常區之太空系統的設計與運作提供最佳的參考價值｡ ; The central portion of the South Atlantic Anomaly (SAA) region is approximately located in the geographic latitudes from 10oS to 35oS and in the longitudes from 270oE to 330oE. Geo-magnetic field strength of the SAA region is considerably weaker than those of the other regions for a fixed altitude. The apex height of the SAA magnetic field lines can reach far to the radiation belts and can even be very close to the ring current region during great magnetic storms. Due to the unique magnetic configuration of SAA, charged particles with energy of several Kev to GeV from above reservoirs may precipitate deeper into the SAA atmosphere than those of other regions. As a result energetic particles ionize and/or energize the atmospheric neutrals. The interaction between energetic particle and atmospheric neutrals results in altitudinal changes of ionospheric structures since the ionization processes depend on the energy spectrum of energetic particles and on the composition of upper atmosphere. Moreover, plasma density enhancements in SAA result in horizontal density gradients (thus conductivity gradients) in/near the SAA region, which can in turn generate electric fields. These localized electric fields can redistribute the ionosphere plasma and sometime even produce favorable conditions for the growth of ionospheric irregularities. We plan to make best use of the FORMOSAT-3 data to investigate above ionosphere phenomena in the SAA region. Since their launch in April 2006 FORMOSAT-3/COSMIC satellites have being provided global ionospheric profiles derived by the radio occultation techniques, and scintillation data computed on orbit from GPS SNR ratio as well as those received by the COSMIC-TBB payload. Uniquely GPS occultation observations can provide data with high vertical resolution of ~ 1 km or better. Because of the easy access of energetic particles into SAA, the ISUAL sensors of FORMOSAT-2, so as many sensors on other satellites, have been purposely switched off when the satellite flew over SAA in order to avoid the particles’ damage. Fortunately, by means of radio occultation technique the COSMIC satellites can continuously provide high vertical-resolution ionospheric density data even within the SAA region. During this proposal period, we will focus on magnetic storm-time events to study the coupling processes and morphologies between energetic particles and ionospheric structures using FORMOSAT-3/COSMIC data. Complementary data from other interplanetary and geo-environmental satellites may also be applied to the proposed study whenever possible. The results of the proposed studies will be extremely valuable not only to the research of Magnetosphere–Ionosphere-Atmosphere couplings, but also to the design and operation of space systems over the SAA region. ; 研究期間 9708 ~ 9807
