摘要 本篇論文利用中華衛星一號上之電離層電漿電動效應儀（IPEI）在西元2000年所觀測到的頂部電離層資料以探討發生在"南大西洋異常區"(簡稱SAA)，經度範圍900W到00E的電漿不規則體結構(plasma bubbles)。先以統計分析此區bubbles的發生機率如何隨不同地方時、季節及地磁擾動狀況而變化。更進一步波譜分析IPEI在兩個具有代表性的衛星軌道上所收集的高解析度(每秒1024筆)離子密度及速度資料，以研究SAA區電漿不規則體在不同尺度的特性。 選定SAA區的觀測資料作為研究，原因之一是此區的磁場特弱，對電漿不規則體的生長率有加強作用。另外因此區的地磁場分佈特殊，華衛一號有機會沿著磁赤道或磁經度運行，增加觀測到bubbles的機率。在統計方面我們發現地磁擾動小時在地方時18~21點會有bubble發生機率最大值，之後機率逐漸減少;而在冬季時bubble發生機率有最大值。地磁擾動大時bubble發生機率大部分在午夜之後;在季節方面，bubble發生機率並不具規則性。在波譜特性方面，我們藉分析密度和速度的功譜密度(PSD)隨波數(k)變化呈現P k-n的關係，且進一歩分析密度波譜指數(nd)與速度波譜指數(nv)符合Boltzmann Relationship(nd=nv+2)，驗證了波長界於100m和15m之間的漂移波(drift wave)存在於近磁赤道的正在成長中的電漿不規則體結構中。 Abstract Data from the Ionospheric Plasma and Electrodynamics Instrument onboard ROCSAT-1 during the solar maximum year of 2000 are used to investigate the plasma depletion (bubble) structures observed in the South Atlantic magnetic Anomaly (SAA) region (40oS ~0oN; 90oW~0oE). We examine how the occurrence probability of the SAA bubbles varies statistically with local time, season, and magnetic activity. Furthermore, we perform the spectral analyses on the high-resolution ion density and cross-track velocity data for two selective passes to investigate the spectral characteristics of the plasma irregularities in the SAA longitude sector. We are interested in the bubble observations in the SAA sector for three reasons. First, the magnetic field in SAA is the weakest among the other places. This may enhance the growth rate of the Generalized Rayleigh Taylor instability that is responsible for the generation of plasma irregularities in the low latitudes. Due to the geomagnetic configuration and the 35o-inclined ROCSAT-1 orbit, ROCSAT-1 may have the opportunity to travel either along the magnetic equator or along the magnetic meridian so as to increase the chances of observing the magnetic field-aligned irregularities. From our statistical study of the SAA bubbles, we found that the bubbles were most often seen in the 18-21 local time sector and in the north hemisphere winter during the quiet time. During the storm time, however, most of the bubbles were observed in the post-midnight sector and can be found in all seasons. We investigate if the power spectral density (P) of irregularities vary with wave number (k) in the form of P µ k-n (power law). We calculate the spectral index “n”, and examine if the relationship between the spectral index (nd) of ion density fluctuations and the spectral index (nv) of velocity fluctuations is the Boltzmann Relationship (nd = nv +2) to verify the existence of drift waves in the growing bubbles near the magnetic equator.
