電離層散塊E層3公尺不規則體凍結效應之研究

A study of Frozen-in property of 3-m plasma Irregularities in Ionospheric Sporadic E layer

鄭倩敏(Chin-Min Tee)

指導教授 ： 朱延祥

國立中央大學/地球科學學院/太空科學研究所/碩士(2006年)

摘要

本文利用中壢特高頻雷達觀測電離層散塊E層不規則體的頻譜特徵估計其在東西方向上的速度分量。由雷達干涉法定位配合moment method 所求得的回波功率、平均都卜勒速度與頻譜寬，可以更進一步分析不規則體在三度空間回波區當中飄移的特性。分析資料過程中發現在不規則體回波的都卜勒速度,會隨著不規則體的東西方向上偏離波束主軸的夾角增加而成一正相關的關係,因此我們可以假設都卜勒頻寬加寬的現象有可能是因為不規則體在橫過波束主軸方向上的飄移所產生的波束加寬效所造成.在這篇論文當中討論到計算最適合計算水平飄移速度四種最小平方趨近法, 其中由實際高度所獲得的水平飄移速度是最合適的.我們使用這種方法來求出來理論徑向速度並將此速度與實際觀測到的都卜勒速度比較發現,兩者的相關性非常好(大於 0.8), 而且相減後根均方值都介於1-3(m/s)之間. 這表示了在1997/8/8這天的某段資料當中, 波束加寬效應對回波速度的貢獻扮演著相當重要的角色。

關鍵字

電離層

並列摘要

The effects of along and transverse radar beam drifts of sporadic E field-aligned irregularities localized in the expected echoing region on mean Doppler velocity and spectral width are theoretically investigated in this thesis. Detailed analysis shows that the Doppler velocities are nearly linearly proportional to the mean angular distance of the irregularities from the radar beam axis decreases with the increase of the horizontal dimension of the plasma structure. Therefore it suggests that the beam broadening effect caused by the drift of the field-aligned irregularities across the radar beam in the geomagnetically zonal direction may play a role in broadening the Doppler spectral width. Four different algorithms for best fitting plasma irregularity data to theoretical expression are discussed here to obtain the optimal solution of transverse beam drift velocity. In order to facilitate mathematical manipulation, the comparison between estimated radial velocity and observed Doppler velocity is made and correlation analysis is also discussed in the articles. In a special case, however, the correlated coefficient between observed Doppler velocity and estimated radial velocity can be as large as 0.8 or more; and the Root-mean-square (RMS) error is in the range of 1 – 3 (m/s). We find that the algorithm of the least squares fit in terms of radar spectra at fixed height for long duration will result in the best solution for the estimation of transverse beam drift velocity. It is easy to see that the beam broadening effect caused by the drift of the field-aligned irregularities across the radar beam in the geomagnetically zonal direction do play a role in broadening the Doppler spectral width.

並列關鍵字

sporadic E irregularities

參考文獻

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