過去研究發現夜間時中緯度電離層有電子濃度增強之現象稱之為中緯度夜間增強現象。本論文首度利用2002年至2009年全球電離層圖之全電子含量(Total Electron Content, TEC)研究發現電子濃度不僅在夜間增強，日間亦會有增強現象，因此命名為中緯度電子濃度增強(Mid-Latitude Electron Density Enhancement, MEDE)。在此定義了中緯度電子濃度增強現象並探討物理機制，詳細研究其發生率和強度之日變化、季變化、緯度變化與太陽活動變化。統計結果顯示中緯度電子濃度增強大多發生2200-0600 LT，強度於0400 LT達到最強。南、北半球電子濃度增強分別落於15¬-52.5?S與25-50?N，而冬季半球較夏季半球容易發生且隨太陽活動增強更為明顯。由於日落反轉現象造成電離層夜間電子濃度增強，故中緯度電子濃度增強現象主要發生於夜間，其受磁赤道效應影響平行於磁赤道，而冬季半球較易發生之情形則與冬季異常現象行為一致。Previous studies presented the mid-latitude ionospheric electron density enhancement in night time, known as the Mid-Latitude Evening Increase. In this study, we first time investigate the mid-latitude electron density enhancement (MEDE) using the TEC (total electronic content) in GIM (global ionospheric maps), and we found that the electron density enhancement not only occurs in the nighttime but also during the daytime, so called the MEDE. Thereinafter, we first define the definition of the MEDE, and further explore the possible physical mechanism, of the occurrence and strength of diurnal, seasonal, latitudinal and solar activity variations. The results show that MEDE mainly occurs during 2200-0600 LT, the strength reaches maximum at 0400 LT. The MEDE is mainly located within 15-52.5°S and 25-50°N. It is more frequently occurs in the winter hemisphere than that in the summer hemisphere, and the occurrence and intensity of the MEDE is proportional to the solar activity. Owing to the prereversal enhancement results in the ionospheric electron density enhancement at night, therefore the MEDE mainly occurs during the nighttime. The location of MEDE are parallel to the magnetic equator and controlled by the geometry of the magnetic equator. The behavior of the MEDE in the winter hemisphere is consistent with the Winter Anomaly.
