| 摘要(英) |
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.
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