本研究擬利用地面同相散射雷以及福爾摩沙衛星三號的GPS電波掩星法(GPS Radio Occultation)，觀測並研究電離層場列不規則體(Field-aligned Irregularities)的空間尺度特性。地面HF/VHF雷達的布拉格背向散射回波(Bragg Backscatter)所觀測到的電子密度不規則體所對應的尺度為1-100公尺，而造成福爾摩沙衛星三號GPS訊號振幅閃爍(Scintillation)的電離層不規則體尺度則為公里級。理論與實驗結果均顯示前者為場列不規則體，回波方位角(Aspect Angle)在0.5以內，至於後者公里級的電子密度不規則體是否具有場列特性(Field-aligned Property)，到目前為止，學術界尚未有具體研究結果。本計畫擬根據福爾摩沙衛星三號GPS電波掩星過程中所觀測的GPS信號振幅閃爍現象，分析閃爍指數(Scintillation Index)的大小是否與GPS射線與地球磁力線夾角有關，探討電離層公里級不規則體的場列特性是否存在。另外並配合地面雷達對於公尺等級場列不規則體的觀測，研究公里與公尺等級不規則體的關係，以及與非線性亂流傾瀉(Nonlinear Energy Vorticity Cascade Process)機制特性。 ;In this study, an attempt is made to study the scale size property of the field-aligned irregularities by using GPS radio occultation of the FORMOSAT-3 satellites combined with the ground-based radar measurement. It is well-known that the scales size of the plasma irregularities responsible for the Bragg backscatter echoes of the coherent scatter radar is meter scale, and the size of the electron density irregularities responsible for the GPS amplitude scintillation is about kilometer scale. Theoretical and experimental results both show that the meter-scale electron density irregularities observed by the ground-based coherent scatter radar are field-aligned irregularities with aspect angle less than 0.5. However, it is uncertain that whether the kilometer-scale electron density irregularities have field-aligned property or not. In this project, we plan to use GPS scintillation data observed by FORMOSAT-3 satellites during the course of radio occultation to study the field-aligned property of the electron density irregularities at kilometer scale. The scintillation index is compared with the angle made by GPS ray and geomagnetic field line from IGRF model. Their relation is analyzed and modeled by a mathematical function using regression analysis. The plasma turbulence strength of the radar-measured meter-scale field-aligned irregularities, which is represented by spectral width of the Doppler spectral width of the radar returns, is compared with the COSMIC-measured GPS scintillation index to study the potential non-linear turbulence energy cascade process in the Kolmogorov turbulence power spectrum.
