利用福衛一號的資料探討磁暴期電離層之擾動發電電場

林彤珈(Tung-Chia Lin)

指導教授 ： 黃健民

國立中央大學/地球科學學院/太空科學研究所/碩士(2014年)

摘要

磁暴期地球電離層受到諸多太陽的間接影響，透過磁力線，電場、電流與各種擾動進入磁層、高緯度電層，最後可將影響傳遞至低緯度地區的電離層，其中擾動發電機制(disturbance dynamo)的效應在磁暴發生後可持續數小時至數天，其影響為在低緯度地區的電離層累積電荷，並產生擾動電場：白天為西向、夜間為東向，方向與安靜期電離層電場相反，本研究主題為透過福衛一號的衛星資料分析，與數值模擬的結果進行比較。
本文討論2000年至2003所有DST小於-140之磁暴事件，總共23個事件進行福衛一號的資料分析，每個事件皆取磁暴發生前兩天與磁暴發生後進行比對，以瞭解磁暴對低緯度地區影響之逐日變化，分為兩個時段來看：當地時間(LT)00至12與當地時間12至24，來討論清晨時期與黃昏時期擾動電場的極值，範圍在南北磁緯度30度以內的低磁緯度地區，其中有17個事件可在日出前發現東向擾動電場，部份事件可在磁赤道地區看到清晨時期有東向擾動電場極大值，與數值模擬結果一致；日側擾動電場並不明顯，與數值模擬結果一致，然而衛星資料中黃昏時期並無明顯西向擾動電場極大值，其可能原因為數值模擬假設日落反轉增強效應(pre-reversal enhancement)存在，實際上此效應並非一定會發生，且有季節性變化。
透過衛星資料的分析，與數值模擬結果比較、討論，來瞭解磁暴期擾動發電機制對低緯度地區電離層的影響。

關鍵字

電離層 ； 擾動發電 ； 電場 ； 低緯度 ； 磁暴

並列摘要

The earth’s ionosphere is under the direct and indirect influence from the sun. Electric currents, fields and other effects can penetrate into magnetosphere and high latitude ionosphere through magnetic field lines. These effects can be transported to low latitude ionosphere eventually. One of these mechanisms, disturbance dynamo, lasts for few hours to few days, with accumulation of positive charges in the low latitude ionosphere. The directions of corresponding disturbed electric fields are westward in the daytime and eastward in the nighttime, opposite to the quiet time condition. The thesis is to do a comparison between model results and observed data from Formosa-1.
There were 23 storms with DST indexes lower than -140 from 2000 to 2003. Every event was analyzed with data from Formosa-1. Two days before the onset of a storm were compared with the storm time to see day to day variations. Every section of singular-orbit-data was separated into two parts at noon time (1200 LT) to find the peak value of electric field at around dawn and dusk. The boundary is set to ±30 degrees in magnetic latitude. Eastward disturbed electric fields were found before dawn in 17 events among all the 23 events .Maximum peak values were found in some of these 17 events. These disturbances are identical to model results. In the contrary, neither the eastward disturbed electric field in the daytime nor the peak value at dusk was found in observed data while model results predicted their existence. This inconsistence could be resulted from the assumption that pre-reversal enhancement existed. In fact, this phenomenon doesn’t occur every day and varies with season.
We can find out how disturbance dynamo affects low latitude ionosphere in the storm time through the comparison and discussion between satellite data and model results.

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