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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/71388


    Title: Tidal Variability Due to the Quasi-Biennial Oscillation and Ionospheric Responses
    Authors: 王傑;Wang,Jack Chieh
    Contributors: 太空科學研究所
    Keywords: 準雙年震盪;電離層;全電子含量;大氣潮汐;Quasi Biennial Oscillation;Ionosphere;TEC;TIE-GCM;Atmospheric Tides
    Date: 2016-07-15
    Issue Date: 2016-10-13 12:55:14 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 準雙年震盪(Quasi-biennial oscillation)為低緯度中層大氣層最主要的震盪現象之一。其成因是來自於熱帶地區的大氣波,包括重力波、開爾文波、羅斯比-重力波,因為具有向上傳播的特性,在平流層對背景風場進行加速作用,使得低緯度的中層大氣物理量具有週期為26到28個月的震盪。例如,在緯向平均、緯向風場中,可以觀察到東、西向風場以近似兩年的週期性交替出現。同時,在高層大氣(高度約為90-120公里,位於中氣層及熱氣層底部)具有主要影響的大氣潮汐也會受到準雙年震盪的調幅。例如,週期為24小時的大氣全日潮,目前普遍認為起源於中層大氣的低緯度地區,在大氣全日潮的發源階段,便會因為都卜勒效應,使貢獻於大氣全日潮的大氣波波長,在經過中層大氣時,受到具有準雙年震盪特性的緯向平均風場調幅,進而影響大氣全日潮的振幅大小。

    根據Chen(1992)的研究指出,在平流層觀察到的準雙年震盪現象,也會一併影射到電離層,使電離層產生類似準雙年震盪的週期震盪現象。這代表了平流層及電離層之間,透過大氣波耦合反應,有可能產生相似的反應。我們已經知道,準雙年震盪最主要的影響,就是表現在緯向平均、緯向風場之中。如果我們將太陽同步遷移的全日潮及半日潮潮汐風場結構,置入TIE-GCM模型的下邊界環境(高度為97公里),便可以觀察到潮汐如何影響到熱氣層的中性風,進而發揮類似攪拌的效果,使得位在400公里高的電離層,電子濃度降低,中性分子的氧原子對氮分子的比值也跟著隨之降低[Yamazaki et al, 2013]。綜合了觀測及實驗結果,我們很好奇,在Chen(1992)電離層的實際觀測中,所看到的準雙年震盪結構,是否可以透過在下邊界條件放置不同準雙年震盪相位所擁有的緯向風場結構,而在TIE-GCM模擬出來實際觀測到的電離層構造。

    在此次研究之中,首先根據與TIMED衛星資料同化的數值模型實驗,發展出太陽同步遷移大氣潮汐的經驗模型。利用大氣潮汐經驗模型中準雙年震盪參數的調整,我們可以量化中層大氣的準雙年震盪對於大氣潮汐之貢獻值。接著利用TIE-GCM模型執行電離層數值實驗,觀察電離層對於大氣潮汐經驗模型在準雙年震盪調幅之下如何響應。同時,利用多維總體經驗模態分解法(Multi-dimensional Ensemble Empirical Mode Decomposition),將近似兩年週期的太陽F10.7指數分量分析出來,一併放置入TIE-GCM模型之中。利用這個方法,我們可以同時觀察來自上邊界的太陽活動及下邊界的大氣潮汐,在同時具有準雙年震盪的特性之下,對於電離層的貢獻。

    我們的研究結果發現,在太陽活動極大期,太陽的準雙年震盪對於電離層的兩年週期震盪具有主導性的地位。而在太陽活動極小期時,具有準雙年震盪特性的太陽活動及大氣潮汐,對於電離層的兩年週期震盪現象效應相當。;The Quasi-biennial Oscillation (QBO) is a persistent oscillation in the zonal mean zonal winds of the low latitude middle atmosphere that is driven by breaking planetary and gravity waves, with a period near two years. The atmospheric tides that dominate the dynamics of the mesosphere and lower thermosphere region (MLT, between heights of 70 to 120 km) are excited in the troposphere and stratosphere, and propagate through QBO-modulated zonal mean zonal wind fields. This allows the MLT tidal response to also be modulated by the QBO, with implications for ionospheric/thermospheric variability. Meanwhile, interannual oscillation in solar radiation could directly drive the variations in the ionosphere with simultaneous period through the photoionization. Many studies also revealed the connection of the solar activities and QBO signal in ionospheric features, e.g. total electron content (TEC).

    In this research, we develop an empirical model to isolate stratospheric QBO-related tidal variability in the MLT diurnal and semidiurnal tides using values from assimilated TIMED satellite data. Tidal fields corresponding to stratospheric QBO eastward and westward phases, as well as the artificial solar forcing with QBO period decomposed by Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD) analysis from Hilbert-Huang Transform (HHT), are then used to drive the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM).

    The numerical experiment results indicate that ionospheric QBO is mainly modulated by the solar QBO by during the solar maximum, since the solar QBO would reach its maximum synchronized with solar cycle. During solar minimum, the ionospheric QBO is modulated from below and above by the stratospheric QBO and solar QBO simultaneously.
    Appears in Collections:[太空科學研究所 ] 博碩士論文

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