Comparison of Interannual Oscillations in the F, E, and D‐Region Ionosphere Using Longterm Ground‐Based Measurements

Abstract This comprehensive study focuses on interannual oscillations from 1 to 25 years in the F, E, and D region ionosphere. By leveraging longterm (1960–2018) continuous ground‐based ionosonde and phase height measurements in northern Germany, we have identified the peak periods and temporal variations of these oscillations using advanced analysis techniques such as Lomb‐Scargle periodogram, wavelet, and coherence analysis to the detrended and deseasonalized data. Our investigation also includes an in‐depth analysis of solar proxies (F10.7 cm and L) to gain insights into the underlying sources of these oscillations. Our results strongly indicate that solar forcing is pivotal in driving oscillations with periods longer than 7 years in the F, E, and D region ionosphere. Furthermore, we have uncovered that the oscillations observed in ENSO‐like and QBO‐like periods are influenced by solar forcing through ionization and lower atmospheric variability through vertical coupling at different time intervals.