| 摘要: | 本文主要利用福衛一號衛星之日地酬載電離層電漿電動效應儀(Ionospheric Plasma and Electrodynamics Instrument，簡稱IPEI) ，在西元2000至2002年(正值太陽活動極大年)，地磁寧靜期(Kp?3)的觀測資料，針對季節、經度、地方時、地磁活動、太陽活動、地磁偏角(magnetic declination)，地面天氣系統等影響電漿泡發生的因素進行逐項探討。 針對全球電漿泡發生率的統計分析，獲得衛星所在的600公里高度頂部電離層，電漿泡發生率隨季節、經度、緯度、地方時、太陽活動期(F10.7)等因素的變化情形。尤其，對於全球電漿泡發生的季節特徵最為明顯的，涵蓋南大西洋磁場異常區（Southern Atlantic magnetic Anomaly，簡稱SAA）之大西洋經度區域和太平洋經度區域，都已獲得電漿泡發生機率分析結果。兩經度區域的特徵比較，有助於瞭解電漿泡發生的機制。 針對赤道區電漿泡發生機率與電漿垂直漂移速度(等同於緯向電場)之相關性研究，發現電漿泡開始發生在地方時1900LT前後，約在緯向電場反轉(prereversal enhancement)後0.5至1小時之間。進一步研究四季反轉峰值與當地時的關係，判定大尺度電漿泡結構發生所需之向上離子漂移速度門檻值(threshold level)為20 m/sec。 透過對於赤道區頂部電漿泡與低層大氣間熱帶輻合區(Intertropical Convergence Zone，簡稱ITCZ)之關聯性研究，發現電漿泡的季節極大發生率區與間熱帶輻合區劇烈降水區幾乎完全相符。並且這種空間的關連性不只是存在於季節平均數據所獲得的結果，也存在於月平均分佈圖型。作者利用2001年1月與2002年1月發生率分佈圖型，發現兩者間明顯的差異，與該兩年1月在巴西東北岸的雨量異常現象一致，成為低層大氣可以顯著的影響頂部電離層電漿泡發生的新證據。 從上述離子密度、離子速度和間熱帶輻合區間的正向關連性，支持作者提出的低層大氣間熱帶輻合區的位置，和F層電漿向上離子速度的大小(?20m/s)兩者，都是影響早期日落後大尺度電漿泡發生的重要因素。 Quiet time ion density depletions observed by the ROCSAT-1 IPEI payload during the solar maximum years of 2000-2002 were used to statistically study the effects of many parameters which are responsible for the generation of plasma bubbles. We examine how the occurrence rates of plasma depletions (bubbles) vary with local time, season, longitude, solar activity, magnetic activity, local magnetic declination, and weather system. Based on the morphology of plasma bubbles, we investigate the dependencies of bubble occurrence rates on season, latitude, longitude, local time, solar flux activity of topside ionosphere. In particular, we focus on the SAA longitude sector (270°E-360°E) and the Pacific longitude sector (150?E - 240?E), where the seasonal and longitudinal variations of the bubbles are most pronounced. The characteristic differences between the two longitude sectors will be helpful to reveal the mechanisms that generate plasma bubbles. We have examined the relationship between plasma depletions and upward ion drifts and found that the time of bubble onset is typically at local time ~ 1900 LT, about half to one hour after the post-sunset enhancement. We further studied the correlation between the pre-reversal peaks and the local times for all seasons to determine the threshold values of the upward ion drift (? 20 m/s) required for the occurrence of large-scale bubble structures. By investigation of the relationship between topside ionospheric plasma depletions and Inter-Tropical Convergence Zone (ITCZ), we found that the maximum occurrences of seasonal bubble structure are almost all collocated with the most intense rainfall regions of ITCZ. Such spatial correlation exists not only in the seasonal averaged data but also in the monthly averaged patterns, which is demonstrated by comparing the monthly bubble occurrence pattern of 2001 January with that of 2002 January. Significant differences in the bubble morphology between the two months were found to closely relate to the precipitation anomalies along the northeast coast of Brazil during the two different years, which provides further evidence that low altitude atmosphere can significantly affect the occurrence of the topside ionospheric plasma bubbles. The positive correlations among the spatial distributions of ion density, ion velocity and ITCZ suggest that both the location of ITCZ and the magnitude of upward ion drift (> 20 m/s) are the main factors to affect the occurrence of large-scale bubbles at early post sunset hours. |
