利用福衛三號資料研究非洲地區閃爍現象與閃電之相關性 ; Using COSMIC/FORMOSAT-3 data to study the relationship between radio scintillation and lightning phenomena in the Africa region

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题名:	利用福衛三號資料研究非洲地區閃爍現象與閃電之相關性;Using COSMIC/FORMOSAT-3 data to study the relationship between radio scintillation and lightning phenomena in the Africa region
作者:	黎東華;Dong-Hua Li
贡献者:	太空科學研究所
关键词:	福衛三號;閃爍現象;閃電;FORMOSAT-3;radio scintillation;lightning phenomena
日期:	2010-07-25
上传时间:	2010-12-09 10:50:39 (UTC+8)
出版者:	國立中央大學
摘要:	由TRMM / LIS及MicroLab-1 / OTD觀測資料中顯示，非洲地區發生閃電事件之年平均分布與季節性平均分布圖中，皆屬閃電好發區，因此本文將探討此區發生之閃電現象與利用福衛三號所觀測到強閃爍現象之關連性。本論文使用福爾摩沙衛星三號Level–1閃爍資料 (scnLv1) 與TRMM / LIS閃電資料進行分析，根據閃爍資料提供之閃爍強度指數(S4)我們可判斷閃爍現象之強弱，而TRMM / LIS提供之閃電發光強度(Radiance)則為本文探討閃電強度之依據。從分析閃爍現象於時空上之變化，發現其閃爍現象與F層不規則體分布時間一致，皆發生於F層底部以及日落後至午夜時段，而季節性之分布也與因磁偏角與日落線間交角關係所造成之不規則體相符，即於北半球夏季(J month)集中於中太平洋經度範圍磁赤道一帶，而北半球冬季(D month)則集中於大西洋經度範圍一帶，但於夏季非洲及其與大西洋交界一帶所觀測到之閃爍現象則非由此機制所產生。而經由比較非洲地區閃爍現象與閃電之冬夏變化情形，發現兩者之南北移動皆在地理緯度範圍之間，因此認為非洲及其與大西洋交界一帶所觀測到之閃爍現象可能與此區為閃電好發區有關。最後將此區近乎同步觀測之閃爍資料與TRMM / LIS閃電資料進行比較與量化分析，發現在福衛三號觀測到的強閃爍現象之前，TRMM / LIS於鄰近位置也觀測到閃電現象，且發光能量(Radiance)皆大於平均閃電之觀測值。根據結果推論此區由閃電所產生之電場，可能為造成閃爍現象的原因之ㄧ。Abstract The annually and seasonally averaged distributions of the lightening activity from TRMM/LIS and MicroLab-1/OTD observations all show that the lightening phenomenon most often occurred in the Africa region. This thesis investigates the relation between the lightening phenomenon and the ionospheric scintillation phenomenon in this region by analyzing the TRMM/LIS lightning images and FORMOSAT-3 scnLv1 data. We use amplitude scintillation index S4 data provided by FORMOSAT-3 to indicate the intensity level of the scintillation events and the radiance data provided by TRMM/LIS to reflect the intensity level of the lightening phenomenon. By analyzing the temporal and spatial variations of scintillation, we found that the local time (LT) distribution of scintillation resembles to that of ionospheric F-region irregularities. They both occur at sunset to midnight hours. The seasonal changes of scintillation distribution agree well with those of F-region irregularity. This is consistent with the mechanism that the post sunset irregularities occur favorably in the region where the angel between magnetic declination and sunset line is small. These favorable conditions imply that the scintillation events concentrate in the central Pacific longitude sector along the magnetic equator in the northern summer, while the events concentrate in the Atlantic longitude sector in the northern winter. However, we notice that the scintillation events found in Africa and its vicinities adjacent to the Atlantic Ocean during the northern summer can not be explained by the above mentioned mechanism. Moreover, the analysis of the seasonal variation of scintillation and lightning in Africa reveals that both scintillation and lightning move in the range of ±30° geographic latitudes depending on the seasons. Therefore we suggest that the lightning activity can be the triggering source of the scintillations observed in the Africa coastal region along the Atlantic Ocean. Finally, from quantitative analyses of the nearly simultaneous scintillation data and the TRMM/LIS lightning data for this region, we find that before observing strong scintillations by FORMOSAT-3, the TRMM/LIS did observe strong lightning phenomenon at neighboring locations, and the lightning radiance is greater than the average observed value of lightning intensity. Based on these results, the electric fields associated with the lightning processes at this region may well cause the scintillation phenomenon.
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