中壢特高頻雷達散塊E層回波都卜勒速度切的統計

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題名:	中壢特高頻雷達散塊E層回波都卜勒速度切的統計
其他題名:	The Statistics of Doppler Velocity Shear in Chung-Li Vhf Radar Sporadic E Echoes
作者:	王建亞
貢獻者:	物理系
關鍵詞:	散塊E 中性風切重力波電子密度不規則體中壢VHF雷達平均都卜勒速度都卜勒速度切回波功率
日期:	2011~2012
上傳時間:	2012-02-22 09:00:46 (UTC+8)
摘要:	中緯度散塊E現象，學者一致認為層狀結構是由中性風切作用所形成，研究顯示向上傳播的重力波擾動中性風是造成中性風切最可能的方式，理論發展及火箭實驗，已經說明這種重力波伴隨擾動中性風的作用，可以在Es層內產生一個夠大的極化電場(Gelinas et al., 2002)，並使電子密度不規則體受ExB作用產生漂移。由於要能形成密度增加的離子層，離子垂直向速率的變化必須為負，才能有收斂的作用，在北半球最有效的情況為上層的風為向西而下層風向為向東，由於在高度100公里附近E層環境的條件，上層西向風(下層東向風)產生向東(向西)的極化電場；受電場作用雷達偵測的小尺度場列不規則體，產生向雷達波束指向靠近(都卜勒速度為負)或遠離漂移(都卜勒速度為正)。本計畫目的在於利用中壢VHF雷達干涉定位的功能，計算同一高度層內不規則體回波所對應的平均都卜勒速度，由上下層的都卜勒速度切與回波功率等的統計關係研究Es現象。 It is generally thought that the neutral wind shear plays an essential role in the formation of the mid-latitude Es layer. One of the most common and efficient ways to produce neutral wind shear is the upward propagating tidal and gravity waves. It has been theoretically and experimentally shown that gravity wave-associated neutral wind may generate polarization electric field inside Es layer owing to differential collisions between neutral-ion and neutral electron pairs ( Gelinas et al., 2002). The wave-induced polarization electric field will give rise to the drifts of ions and electrons in the Es layer through ExB effect. In order to fulfill the convergence requirement of the plasma for the Es layer formation in northern hemisphere, the wave-associated zonal neutral wind in upper (lower) portion of the Es layer should be in the west (east) direction. Note that in lower E region below about 130 km Hall conductivity is appreciably larger than Pedersen conductivity. In this environment, because ion-neutral collision frequency is comparable to ion gyro-frequency and electron-neutral collision frequency is much smaller than electron gyro-frequency, one might expect that the westward (eastward) neutral wind will be responsible for eastward (westward) polarization electric field. In the presence of meter-scale FAIs, VHF coherent scatter radar will detect echoes from upper (lower) Es layer that will have mean Doppler velocity away (toward) the radar. As a result, the gravity wave-induced polarization electric field in the Es layer can therefore be estimated from the radar-observed Doppler velocity that is primarily caused by the ExB effect. In this proposal, the Doppler velocity shear will be derived from the radar interferometry and find the characteristic relation to radar echoes.
顯示於類別:	[光電物理系] 研究計畫

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