Climatology of the spread F over Roquetes, Spain: Impact of the medium scale traveling ionospheric disturbances

Abstract

Understanding the long-term variability of nighttime Spread F (SF) and its drivers is crucial for improving the knowledge of ionospheric disturbances, which impact radio communication, GNSS positioning, and space weather forecasting. This study exploits the long-term ionogram dataset from the EB040 ionosonde in Spain (1955–2022) to investigate the climatology of nighttime SF and its dependence on solar activity. We analyze the diurnal, seasonal, and solar-cycle variability of both Range Spread F (RSF) and Frequency Spread F (FSF). The results reveal a strong inverse relationship between SF occurrence and solar activity, with SF maxima during solar minima. SF is confirmed as a predominantly nighttime phenomenon in western European mid-latitudes, primarily occurring between 20:00 and 05:00 UT, peaking near the solstices, with higher occurrence in June–July than in December–January, and with RSF accounting for 69% of SF events. Complementary analysis using GNSS-derived detrended Total Electron Content (d-TEC) and Rate of TEC index (ROTI) maps (2012–2016) quantifies the connection with Medium-Scale Traveling Ionospheric Disturbances (MSTIDs). Approximately 85% of SF occurrences at EB040 coincide with MSTID activity, with correlation coefficients above 0.96 between their onset times. MSTID activity exhibits the same seasonal pattern as SF, peaking at the solstices—particularly in June–July—and displaying the same inverse dependence on solar activity. Furthermore, 62% of RSF events at EB040 are associated with strong ROTI activity, especially during summer, and 83% of RSF events lasting over two hours correspond to strong ROTI activity. Overall, these findings highlight MSTIDs as the dominant electrodynamic driver of mid-latitude SF and underline the seasonal and solar activity dependencies of SF variability, providing new constraints for understanding ionospheric dynamics.