Distribution Characteristics of Nighttime MSTIDs over China and Their Connections with Mid-latitude Spread-F

This study investigates the spatiotemporal characteristics of periodic Total Electron Content (TEC) disturbances associated with Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) over the Chinese sector and examines their statistical relationship with Mid-latitude Spread-F (MSF). MSTIDs and MSF are two common ionospheric phenomena occurring at different spatial and temporal scales in the midlatitude F region, and previous studies have suggested that they may be dynamically connected. To clarify this relationship, we use observations from more than 250 Global Navigation Satellite System (GNSS) stations of the Crustal Movement Observation Network of China (CMONOC), together with ionogram data from four ionosonde stations operated by the China Research Institute of Radiowave Propagation (CRIRP). A statistical analysis is conducted to characterize the occurrence, temporal variability, and spatial distribution of nighttime MSTIDs from 2014 to 2023, with particular attention to summer conditions and their association with spread-F events. The results reveal clear solar-cycle and seasonal dependences of MSTID activity in the Chinese sector. Their occurrence rates are substantially higher during solar minimum years than during solar maximum years, and the disturbances occur most frequently during summer nights. Spatially, two distinct regions of enhanced MSTID occurrence are identified, suggesting the influence of different generation mechanisms. The characteristics presented by the eastern peak are basically consistent with those driven or amplified by the MSTIDs associated with the Perkins instability and its related electrodynamic processes. In contrast, the western peak is closely associated with frequent atmospheric gravity wave activity southeast of the Tibetan Plateau, where complex terrain and active convection may provide strong wave sources. Further analysis shows that MSTIDs and MSF frequently occur on the same night and exhibit a relatively stable temporal sequence, with MSTID activity generally preceding the onset of MSF. This chronological relationship suggests that MSTIDs may create favorable conditions for spread-F development by perturbing plasma density gradients, modifying the bottomside F layer, or enhancing polarization electric fields. Although the statistical results do not by themselves establish direct causality, they provide important observational evidence supporting a possible triggering or preconditioning role of MSTIDs in the generation of MSF. These findings improve our understanding of multiscale coupling processes in the midlatitude ionosphere.