台灣地處電離層赤道異常區，最大電漿頻率foF2居全球之冠， 本論文利用電離層探測儀，探討台灣地區上空foF2特性與太陽週期間之變化。統計分析第廿一和廿二太陽活動週期，1976-1996，間的觀測資料，得知foF2日變化中出現一年雙峰頻次於午後最為明顯且與電離層電子密度之日變化呈現正相關；年變化方面，雙峰出現頻次與太陽活動及電子密度之年變化也皆呈現正相關。各季極值變化與太陽活動性一致，惟獨夏季極值與太陽活動相關性在0600 LT後較為特出，與另三季極值變化皆相反。各季foF2極值差距除春季減冬季與秋季減冬季外，皆與太陽黑子數呈正相關。而各極值於一年中出現日期則較不受太陽週期影響。 Taiwan is right under the equatorial ionization anomaly, EIA, region, and therefore it yields the greatest value in the critical plasma frequency foF2 of the world. This research examines solar activity variations in the foF2 recorded in Taiwan. A statistical investigation of the foF2 during the solar cycle 21 and 22 reveals that the foF2 yields pronounced maximum values in the spring and fall during the post noon period. The appearance of the two maximum is approximately proportional to the diurnal variations of the foF2. Meanwhile, the appearance of the two maximum is found to be in proportional to the solar activity and the yearly mean of the foF2. Variation of the maximum value in the spring and fall, and the minimum value in the winter are similar to those of the solar activity except the summer. Difference between the extreme generally are proportional to the solar cycle variation, expect between spring and winter as well as fall and winter. The appearance dates of the extreme seem not to be a function of the solar activity.