Studying the characteristics of terdiurnal tides in the ionosphere provides an important pathway to understand the dynamic coupling between the low atmosphere and the ionosphere. Based on the TEC data from the Madrigal database at the Massachusetts Institute of Technology Haystack Observatory, a decomposition and nonlinear fitting method is used to derive ionospheric terdiurnal tides. Statistical analysis is then carried out to study the variability of ionospheric terdiurnal tides. Both the absolute and relative amplitudes of terdiurnal tides are large near the equator and in the equatorial ionization anomaly (EIA) region. The relative amplitude of terdiurnal tides in the Northern Hemisphere is larger than that in the Southern Hemisphere at low latitude, exhibiting hemispheric asymmetry. The amplitudes of terdiurnal tides at magnetic middle latitudes (∼35 °N MLat) at the east hemisphere (142 °E), west hemisphere (90 °W) and zero degree longitude sites all have annual, semiannual and 4-month cycles. Furthermore, our analysis shows that there are longitudinal variations of terdiurnal tides and these variations appear to be dependent on solar activity. Terdiurnal tides show two peaks near the equinoxes, one in March and April, and the other between October and November. The terdiurnal tides with characteristics of large amplitudes in the equator and EIA regions, and their correlation with the diurnal and semidiurnal components suggest that terdiurnal tides and their intra-annual variations are likely related to the nonlinear interaction between diurnal and semidiurnal tides, which also show strong intra-annual variations.

中文翻译：

---

电离层日潮的特征

研究电离层的昼夜潮汐特征为了解低层大气与电离层的动力耦合提供了重要途径。基于麻省理工学院Haystack天文台Madrigal数据库的TEC数据，采用分解和非线性拟合方法推导出电离层日潮。然后进行统计分析以研究电离层昼夜潮汐的变异性。在赤道附近和赤道电离异常（EIA）区域，昼夜潮汐的绝对和相对幅度都很大。北半球晚潮的相对振幅在低纬度地区大于南半球，表现出半球不对称性。东半球（142°E）、西半球（90°W）和零度经度站点的磁中纬度（~35°N MLat）的日潮幅值都有年、半年和4个月的周期。此外，我们的分析表明，昼夜潮汐存在纵向变化，这些变化似乎取决于太阳活动。昼夜潮汐在春分点附近有两个峰值，一个在 3 月和 4 月，另一个在 10 月和 11 月之间。赤道和EIA地区具有大振幅特征的日潮及其与日、半日分量的相关性表明，日潮及其年内变化可能与日、半日潮之间的非线性相互作用有关，这也表明强烈的年内变化。