模擬電離層E層電子濃度與散塊E層的發生機制 ; Model simulation of E region electron density and Sporadic E layers

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题名:	模擬電離層E層電子濃度與散塊E層的發生機制;Model simulation of E region electron density and Sporadic E layers
作者:	林筵捷;Yen-chieh Lin
贡献者:	太空科學研究所
关键词:	連續方程式;解微分方程式;散塊E層;模擬;電離層E層;電子濃度;sporadic E;E-region;runge-kutta;continuity equaiton;electron density;simulation;Model
日期:	2010-07-20
上传时间:	2010-12-09 10:50:43 (UTC+8)
出版者:	國立中央大學
摘要:	本篇論文模擬電離層E層的電子濃度與因風切效應所引發的散塊E層發生機制。為了得知E層的電子濃度，我們利用E層中存在的五個離子(NO+、O2+、N2+、O+、Fe+)濃度加總來推算電子濃度。一開始單純只考慮經由光化學作用(產生作用與消失作用)產生的背景電子濃度分佈，則模擬的方法為：把隨高度、時間變化的離子產生率與離子消失率代入離子的連續方程式，以Runge-Kutta Method來解此連續方程式(一階微分方程式)，如此可得到各個離子濃度隨著高度與時間變化的分佈。接著我們模擬潮汐風場造成散塊E層的發生現象。在E層，因離子碰撞頻率大於離子旋繞頻率，緯向潮汐風可藉由U×B drift導致離子在高度上有上下移動，當上層緯向風為西風、下層緯向風為東風，則會使離子在垂直漂移速度的輻合區域內累積，形成散塊E層。依上述想法，潮汐風造成的離子垂直漂移速度亦即為連續方程式中離子的傳輸項。接著把傳輸項代回連續方程式，以Crank-Nicholson Method來解此連續方程式(二維一階微分方程式)，如此可見因風切效應所造成的散塊E層發生現象。In this study, we not only simulate height-time variations of background electron density of E region ionosphere but also study the formation of Sporadic E layers that is highly associated with the neutral wind shear. In order to model the electron density of E region ,we calculate the densities of NO+、O2+、N2+、O+、Fe+ that are assumed to consist in the ions in E region. The initial condition of the simulation is the photochemical equilibrium in E region, we calculate theoretical production rate and loss rates of the ions and substitude them into continuity equation to solve the first-order partial differential equation in accordance with Runge-Kutta method. We then model the tidal wind that is responsible for the formation of Sporadic E layers. In the lower E region, the zonal neutral wind is the primary factor causing vertical ion drifts, which is the physical process of U×B dynamo in E region. Therefore, it requires that the zonal neutral wind with weatward in upper and eastward in the lower E region will result in ion convergence in northern hemisphere. The Sporadic E layers will occur at the region where the ion converges. With this configuration, the vertical ion drift velocity induced by tidal wind consititudes the transport term in continuity equation. Once the transport term is considered in the continuity equation, we use the Crank-Nicholson method to solve the resulting partial differential equation. The result indicates that a sporadic E layers indeed occurs at the regions where the ion are converged in the node of the neutral wind shear.
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