中華衛星一號上的『日地物理』酬載『電離層電漿電動儀』（IPEI）從1999年1月27日順利發射升空運作至今已有完整的高層電離層離子資料，利用所測到的高解析度資料，採用2000年整年度資料中全球電離層電漿濃度不規則變化區域內離子向下飄移的資料，統計分析這些離子的空間分佈如何隨季節、地理位置及地磁擾動等因素而變化。針對向下運動離子與向上快速運動離子的波譜結構進行分析與比較。分析結果顯示這類事件的發生次數以春秋兩季節較多，其發生位置依磁赤道做南北分佈。由波譜分析此類電漿泡電漿的密度與速度資料，發現在向下運動離子長波的部分與向上運動所得到的結果相去不遠其功譜指數n1（波長大於200 m）介於-1到-2之間，而n2（波長介於15?200 m）則有明顯的差異。向下運動離子並無明顯的區分n1及n2，如有則n2介於-2到-6之間顯示波長小於100 m的結構已消散，相反的快速上升的電漿不規則體短波的結構可達到15 m。在短波方面的功率消散極快顯示所觀察到的電漿泡結構逐漸退化。此外離子向下運動速度大於200 m/s的電漿泡大部分出現在磁赤道兩側（±15°MLAT）而非磁赤道上驗證了電漿不規則一旦發生會沿磁力線分佈。 The ROCSAT-1 satellite was launched on 27 January 1999. The ionospheric plasma and electrodynamics instrument (IPEI) onboard ROCSAT-1 has collected a large set of topside ionosphere data. Using the IPEI data collected during Year 2000 we select the events of density depletion region, in which the ions moved downward, to examine the spatial distribution of these events and their dependences on season and geomagnetic activity (Kp). Furthermore, we analyze the high-resolution density and velocity data to study the spectral characteristics of these events. The results show that these events distributed nearly along the magnetic equator. The density depletion regions with ion’s downward velocity exceeding 200 m/s were most often observed on both sides of, but at latitudes (about ±15° MLAT) far away from the magnetic equator. This confirms that the field-aligned motion of the plasma inside depletion regions. The spectral analysis tells us that the spectral index of depletion structures for wavelengths between 50 m to 200 m is -4 to -6. Such steep spectrum suggests that only weak small-scale structures (wavelength < 200 m) existed. It also illustrates that the observed irregularity structures are decaying.
