Winter Enhancement of the Occurrence and Intensity of the Sporadic-E Layer

In this study, long-term variations in the occurrence rate and intensity of the sporadic-E (Es) layer are investigated using data from the Constellation Observing System for Meteorology Ionosphere and Climate radio occultation and ground-based ionosondes. The results reveal a distinct semiannual variation in Es layer behavior, with a prominent maximum during the summer and a secondary weaker peak during the winter. Additionally, the occurrence rate and intensity of the Es layer reach their minima during the equinoxes, specifically in March/April and September/October. The analysis of quasi-6-day (Q6DW) and quasi-16-day (Q16DW) planetary waves (PWs) in the mesosphere and lower thermosphere region shows notable enhancement during the winter months. This modulation of wind patterns by amplified PWs is suggested to contribute to the winter enhancement of the Es layer. Furthermore, horizontal wind data from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension are used to simulate vertical ion convergence (VIC). The simulation results indicate that VIC peaks in both summer and winter, offering an explanation for the observed semiannual variation in Es layer occurrence and intensity, particularly in the Northern Hemisphere. Spectral analysis of Es layer data reveals that the dominant variations are associated with the annual oscillation, followed by the semiannual oscillation, underscoring the significant role of large-scale atmospheric oscillations in driving Es layer variability.