Midlatitude SF occurrence differences over two European Digisonde stations

The present study examines the diurnal and seasonal variations in nighttime midlatitude spread-F (SF) occurrence over Roquetes and Nicosia during 2014, 2016, and 2020 to explore longitudinal variability over the European area. The significant differences in SF occurrence between these stations are observed and are more pronounced with decreasing solar activity. This variability is attributed to UA-NPD, TIDs, and NW-SE electrodynamic coupling between the Es and F layers. RSF dominates SF occurrence, driven by Es layer instabilities coupled with the F layer. SF occurrence peaks in summer with a secondary maximum in winter at both locations.