Statistical Study on the Connections Between TEC Periodic Disturbances Associated With MSTIDs and Mid-Latitude Frequency Spread F in Summer Nights Over China

In this study, the connections between medium-scale traveling ionospheric disturbances (MSTIDs) and mid-latitude frequency spread F (FSF) during summer nights in the China sector are statistically investigated using data from over 250 GNSS stations and 12 ionosonde stations from 2014 to 2018. First, both phenomena are observed to commonly occur on the same night during summer, with longer durations of FSF corresponding to higher average MSTIDs activity values. MSTIDs activity tends to precede the FSF occurrence. The statistical peak distribution of MSTIDs activity is concentrated before midnight, whereas FSF peaks after midnight, with median occurrence time differing by approximately 1–2 hr. Additionally, FSF and MSTIDs exhibit similar spatial propagation characteristics, with occurrences in the northeastern region occurring earlier in universal time (UT). Building on these findings, the potential physical processes and mechanisms by which MSTIDs may excite FSF are further discussed, including the role of E-F coupling, as well as significant changes in critical frequency and virtual height at different MSTIDs activity conditions. Furthermore, the underlying reasons for the differences in the temporal distribution of FSF at different latitudes are also analyzed. The midnight type FSF may be related to the disturbed electric fields in MSTIDs and gradient drift instability, while presunrise type FSF mainly concentrates at higher latitudes, without obvious connections to MSTID activity, suggesting the existence of excitation mechanisms beyond MSTIDs.