日食提供研究電離層暫態變化之最佳課題。2012年5月21日於臺灣發生日環食。此距前兩次之日環食（1955年12月14日與1958年4月19日）已有六十餘年。本論文利用地面全球定位系統接收機之全電子含量(Total Electron Content, TEC)、福衛三號電子濃度垂直剖線、高頻都卜勒系統之頻移、電離層探測儀之電離圖、雷文送之溫溼度和氣壓高度剖線、特低頻電波之電波強度、特高頻雷達之電離層回波和磁力計之磁場強度，進行2012年5月21日日環食聯合觀測，發現電離層全電子含量減少百分比與遮蔽率成正比，其極端值減少較食甚之延遲時間則隨著離環食中心越遠而越長。電離圖顯示電離層高度在初虧到食既是上升，而後則下降，此與對應之都卜勒探測系統之頻移呈現先負後正相互吻合。特低頻電波強度較平日減小並且出現延遲現象。除雷文送、特高頻雷達及福衛三號外，觀測儀器皆證明電離層有日食效應。

Solar eclipses are a good case study of transient ionospheric changes. An annular solar eclipse was observed in Taiwan on May 21, 2012. This was the first such event in 60 years, with the previous two occurring on December 14, 1955 and April 19, 1958. During those earlier events, there were no scientific instruments for observations and experimentation. However, a wide variety of instruments was used to observe the 2012 event. The effects of the May 21, 2012 eclipse were observed using total electron content (TEC) obtained from ground-based GPS receivers, electron profiles from Formosa-3/COSMIC (F3/C), Doppler shift from the High Frequency Doppler System, ionograms from the National Communications Commission (NCC) ionosonde, tropospheric and stratospheric temperature and pressure profiles from radiosondes, Voltage amplitude of very low frequency (VLF) radio waves, ionospheric echos of very high frequency (VHF) radar, and magnetic fields from a network of Taiwan magnetometers. With the exception of the radiosondes, VHF radar and F3/C, all of the other instruments record clear ionospheric solar eclipse effects.

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