電離層赤道異常區之電子濃度季節性震盪及日變化;Variability of the Equatorial Ionization Anomaly on seasonal and day-to-day time scales

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Title:	電離層赤道異常區之電子濃度季節性震盪及日變化;Variability of the Equatorial Ionization Anomaly on seasonal and day-to-day time scales
Authors:	簡士涵;Chien,Shih-han
Contributors:	太空科學研究所
Keywords:	磁赤道異常;小波轉換;Equatorial Ionization Anomaly;wavelet
Date:	2015-07-15
Issue Date:	2015-09-23 10:47:46 (UTC+8)
Publisher:	國立中央大學
Abstract:	赤道區電離子濃度異常(EIA)是一個發生在電離層F層，也就是在大約300公里高的特有現象，磁赤道兩側的電子濃度在當地時間下午會異常的高，科學界認為主要是受到電離層E層的風場發電機制所衍生，我們在本論文中探討在EIA發生時電子濃度受到太陽活動、地磁活動、大氣活動所產生的短期震盪變化，利用全球電離層地圖探討分別在西經105度、東經15度及120度之EIA發生時的電子濃度，與F10.7太陽射線、地磁活動指數 Kp index及從GAIA assimilative general circulation modal模擬所得到在100公里高分別在中緯度地區與赤道地區的緯向風場所產生的耦合作用，我們對EIA電子濃度及上述提到的物理參數分別在2008年級2012年進行小波轉換分析及討論其相關性以及季節震盪和日變化，我們的結果顯現太陽活動F10.7指數主要有27天週期帳盪。Kp index在2008年由9天週期的震盪所主導，在2012年則是13天與5-7天的震盪分布在特定的季節，原因是因為太陽風的分布差異所致。EIA之電子濃度同樣顯現這些週期性的震盪，並且透過我們的相關性分析呈現了與太陽活動及地磁活動高相關性。對於中性風的研究，我們發現在太陽極大期時(2012年)，赤道區100公里高的緯向風所產生的行星波震盪對於一樣經度的EIA電子濃度具有較大的相關性，而太陽極小期時(2008年)則是中緯度地區的風場震盪影響較為明顯，我們猜測在不同條件下的風場震盪會以不同的方式影響著電離層E層的風場發電機制，我們用新的小波轉換相關性分析方法將對於詳細的EIA短期震盪與正確的發生機制有更進一步的成果。;The Equatorial Ionization Anomaly (EIA) is a persistent feature of the ionospheric F layer, located around 300 km altitude, generated by the E-region wind dynamo driven equatorial fountain. We report our analysis of short term EIA variability due to atmospheric, solar, and geophysical sources. Short-term anomalies in EIA region total electron content (TEC) from GPS-derived global ionosphere maps (GIM) at 105° W, 15°E and 120°E longitude are compared to anomalies in three different geophysical sources: solar flux (F10.7 solar flux proxy), geomagnetic storms (Kp index), and atmospheric mesosphere and lower thermosphere (MLT) zonal winds near the semidiurnal tidal peak at northern mid-latitudes and at the equator (GAIA assimilative general circulation model). We present spectral and coherence analysis of EIA TECs and the aforementioned geophysical indices in 2008 and 2012, to illustrate their variability on seasonal and day to day time scales. Our results demonstrate that the variability of the F10.7 solar flux proxy is dominated by the 27 day solar rotation periodicity at all longitude zones. The Kp index shows significant 9 day periodicities in 2008 for entire year, though 2012 is dominated by significant variations with 13 day periods and 5-7 day periods during specific seasons due to differences in the distribution of solar wind corotating interaction regions (CIRs). The EIA TECs show good coherence with the Kp and F10.7 indicies in all three longitude zones during specific seasons. With regard to the neutral zonal winds, EIA TECs show good coherence with 100 km equatorial zonal winds in the same longitude region at specific known planetary wave periods during the solar maxima, but during solar minimum, 100 km mid-latitude zonal winds exhibit more impact on TECs, suggesting that the MLT latitude region responsible for modulation of the E-region dynamo winds differs between the two years examined.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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