Isual Publications 2014

Isual Publications 2014

  • id
  • date time
    2014-04-08 14:38:00
  • 2009
  • 7
  • 李立柔(2009),‘影響高空短暫發光現象的綜觀尺度因素’,國立成功大學物理研究所(碩士論文)
  • 從1989年紀錄到第一個紅色精靈影像至今,約經過了二十年,在全球許多地方都已紀錄到高空短暫發光現象的影像,且已證實高空發光現象不只是特定區域的現象。藉由ISUAL的衛星觀測資料,我們可以了解高空短暫發光現象的全球分佈情形。從2004年7月至2008年8月間,ISUAL共紀錄到一萬多個高空短暫發光現象。由TLEs四季的全球分佈特性,我們發現TLEs的分佈約略可發成兩區,低緯度熱帶地區(25°S~25°N)及中緯度溫帶地區(30°以上)。我們分別探討影響這兩區TLEs分佈的綜觀尺度因素,並比較兩區內TLEs的發光強度差異。 

      低緯度地區TLEs分佈隨著季節變化,在赤道附近南北移動的現象,我們推測可能與間熱帶輻合區(Inter-Tropical Convergence Zone,ITCZ)的季節移動有關。由分佈位置統計約有84%的TLEs發生於ITCZ範圍內,且不同區間的TLEs和ITCZ有相似的振盪特性,因此可以了解在熱帶地區中,ITCZ是影響TLEs分佈的綜觀尺度因素。 

      中緯度地區的TLEs在冬季時大量出現,且有集中在特定區域的趨勢,所以發生於溫帶地區的TLEs又稱為winter TLEs。先由個案討論,接著比較每日溫帶氣旋中心與winter TLEs分佈位置,最後比較winter TLEs發生率及風暴路徑頻率。在由小至大的空間尺度下都可以發現,溫帶地區冬季TLEs的發生,與溫帶氣旋引發的天氣系統有關。 

      分別分析淘氣精靈及紅色精靈的發光強度,比較熱帶地區及溫帶地區的事件發光強度。分析結果指出,熱帶地區由太陽輻射直接提供能量,造成的輻合對流,較容易引發發光強度較大的淘氣精靈及紅色精靈;溫帶冬季地區由兩種不同性質的氣團互相推擠,造成的動力抬昇對流,較不易引發的發光強度大的淘氣精靈及紅色精靈。

    It has been 20 years since the recording of the first sprite image in 1989. In the past 20 years, TLEs (transient luminous events) have been observed in many geographic locations around the world and these testify that the occurrence of TLEs is a global phenomenon. In this work, we investigate the global distributions of TLEs through analyzing the ISUAL recorded events. Between July 2004 and August 2008, ISUAL payload on the FORMOSAT-2 satellite has registered over ten thousands TLE events. From the seasonal distributions of ISUAL TLEs, they show two distinct distribution patterns; TLEs over the low-latitude tropical region (25°S~25°N) and those over the mid-latitude winter region (greater than 30°). In this work, the synoptic-scale factors of TLE distributions are studied and the luminous intensity of TLEs in the two regions is compared. 

      In the low-latitude region, the distributions of TLEs exhibit seasonal variation and migrate north and south with respect to the equator. We suggest that the seasonal migration of TLE distributions is related to the movement of the ITCZ (inter-tropical convective zones). From correlating the location of TLEs and the distribution of ITCZ, we found that 84% of low-latitude TLEs occurred over the ITCZ and the migrating characteristics of the TLE distribution closely follows that of the ITCZ. Therefore, in the tropical region, we conclude that ITCZ is a key synoptic factor that controls the occurrence of TLE. 

      In the mid-latitude region, the occurrence of TLEs congregates over some specific regions in the winter season. Therefore the TLEs that occur over the winter region are called the winter TLEs. From the case studies that compare the distributions of daily winter storm center and winter TLEs, we realized that winter TLEs are highly correlated to the winter storm. Moreover, the distribution pattern of the winter TLE occurrence density and the storm-track frequency are offset but shows similar pattern. The location analyses we performed all give indication that the occurrences of winter TLEs are correlated with the weather systems induced by winter storms. 

      We also compare the luminous intensity of TLEs from the tropical and winter regions through analyzing the elve and sprite intensities. For TLE over the tropical regions, the events drew their energy from the convective systems that develop from convergence of the wind and, which in turn extract their energy indirectly from the solar radiation; whereas for the TLEs over the winter regions, cold and warm air masses with different properties collide and then the uplift convective systems are developed and eventually produce the winter TLEs. From our analyses, the convective systems in tropical region induce the high intensity TLEs more easily than in winter region.

Wednesday the 17th. ISUAL. All rights reserved.