全球定位系統（Global Positioning System, GPS）地面接收機的優點為能以高時間解析度長期連續觀測電離層全電子含量(Total Electron Content,TEC)，缺點為無法進行海洋和偏遠沙漠等地區之觀測；反之，福爾摩沙衛星一號(FORMOSAT-1)之觀測可均勻涵蓋南北緯35°內，卻無法對固定位置進行連續觀測。本研究結合兩者，聯合觀測1999年3月11日至2004年6月15日太陽活動極大期間南北磁緯30°內電離層不規則體(ionospheric irregularities)的日變化、季變化、經度變化與磁暴的影響。資料分析是利用希爾伯黃轉換(Hilbert-Huang Transform, HHT)的瞬時特性，計算福衛一號正離子濃度數據中週期短於25分鐘波動的瞬時總能。另一方面，使用雜訊輔助篩濾程序(noise- assisted sifting process)去除GPSTEC數據內中尺度移行電離層擾動(Middle Scale Traveling Ionospheric Disturbance, MSTID)的影響，用於計算GPS相位擾亂指數(phase fluctuation index)。最後比較瞬時總能與相位擾亂指數，探討低緯電離層不規則體強度隨時間的改變與空間的分佈，結果顯示不規則體的強度與其產生機率呈正相關。比對44個Dst超過-100的磁暴(magnetic storm)案例與GPS相位擾亂指數長期觀測資料發現，磁暴對於低緯電離層不規則體的成長具有催生和抑制的效應。 A ground-based receiver of the global positioning system (GPS) can easily probe the ionosphere, except desert and oceanic areas, with a high temporal resolution. By contrast, a satellite orbiting observes large area (for example, FORMOSAT-1 covers the ionosphere within +/- 35°) and, however its revisit time generally is rather long. In this study, seasonal and geographical variations as well as geomagnetic storm signatures in ionospheric irregularities within +/- 35° are examined by employing worldwide ground-based GPS receivers and FORMOSAT-1 during the solar maximum period of 1999/1/27-2004/6/17. The Hilber-Huang transform is first applied to compute the instantaneous total power of waves with period less than 25 minutes of the ion density recorded by FORMOSAT-1 and to remove middle and large scale travel ionospheric disturbances (MSTID) in the ionospheric total electron content derived from the ground-based GPS receivers. Results show that the spatial distributions of the FORMOSAT-1 total power generally agree with those of the GPS TEC phase fluctuation in various seasons. Moreover, a long-tern observation in the GPS TEC phase fluctuation indicates that magnetic storms can either trigger or suppress low latitude ionospheric irregularities.
