| 摘要: | 本篇研究使用中壢站(〖25.0〗^o N, 〖121.1〗^o E)超高頻雷達的資料，透過多基線干涉測量分析(multiple baseline interferometry analysis)方法研究中緯度電離層E層中零星不規則體的結構與動態變化。干涉儀測量表明，E層零星不規則體在經向、緯向與垂直方向分布範圍依序為4~12公里、10~28公里與6~14公里。垂直、緯向與經向的E層零星電漿飄移速度以投影至上述立體空間之投影做估計，各別方向之速度落在-15 ~16 公尺/秒、-91~50公尺/秒與-13~26公尺/秒，其中正(負)分別代表向上(下)、向東(西)與向北(南)。分析重力波的頻散關係得知E層中的重力波傳遞方向主要是由西向分量與些許的北向分量構成。此波的週期最大約46.3分鐘且垂直方向、經向與緯向之波長分別落在4~12公里、10~28公里與6~14公里。此外，E層理論極化電場是根據電離層電流系統計算的，理論上推得的經向極化電場大於緯向極化電場。此次研究在重力波破碎的之E層環境中，透過東向的極化電場估計飄移速度並且與雷達觀測之場向不規則體徑向速度做比較。由觀測結果顯示，徑向方向的速度與東向的極化電場所對應之飄移速度一致。因此，在E層不穩定很可能是造成電漿結構變化的主因。此外，干涉儀測量顯示，與重力波傳播相關的電漿結構呈塊狀或羽狀結構，而那些不受重力波干擾的電漿結構呈薄層結構，並以約 2.17 公里/小時的速度隨時間下降.觀測表明，厚度約為 2-4 公里的薄 Es 層的高度可以被高度為 10 公里或更高的重力波影響，造成顯著的改變。;Based on multiple baseline interferometry analysis, we investigated the spatial struc- tures and dynamic characteristics of the 3-m field aligned sporadic E (Es) layer ir- regularities at midlatitude by using Chung-Li VHF radar (25.0o N, 121.1o E). Inter- ferometry measurement demonstrates that the meridional, zonal and vertical extents of the field aligned sporadic E layer plasma structures were approximately in the spans 6 - 14 km, 10 - 28 km, and 4 - 12 km, respectively. The vertical, zonal and true meridional drift velocity of sporadic E plasma structures estimated from the temporal displacement of the plasma patterns projection on three mutually normal surfaces were, respectively, in ranges between -15 and 16 m/s, between -91 and 50 m/s, and between -13 and 26 m/s, in which the positive (negative) sign indicates upward, eastward and northward (downward, westward and southward) drifts. Anal- ysis of the dispersion relation of gravity waves of the trace velocity components of Es layer suggests the presence of majorly westward with slightly northward propagating gravity waves that modulated the Es layer. Evidences shown that the largest gravity wave period is about 46.3 min and the vertical, zonal and meridional wavelengths of the gravity wave is approximately about 12 km, 120 km and 35-40 km, respectively. In addition, the theoretical polarized electric fields of Es layer are calculated from ionospheric current system such that the zonal (i.e., eastward) polarized electric field
was much larger than the meridional polarized electric field. Then, the corresponding drift velocity of eastward polarized electric field is estimated to compare with the radar-observed radial velocity of Es FAI in the environment of gravity wave breaking. The observed radial velocity agree with drift velocity of eastward polarized electric field. Therefore, the gradient drift instability was most likely the physical mechanism governing the dynamic behavior of the plasma structures. Furthermore, interferom- etry observation indicates that the plasma structures associated with gravity wave propagation were in clumpy or plume-like structures, while those not disturbed by the gravity waves were in a thin layer structure that descended over time at a rate of about 2.17 km/hr. The observation demonstrates that the height of a thin Es layer with a thickness of about 2-4 km can be significantly altered by a gravity wave with a height of 10 km or more. |
