Research Article

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

¹ Frederick Research Center, Nicosia 1036, Cyprus
² Department of Electrical Engineering, Computer Engineering and Informatics, School of Engineering, Frederick University, Nicosia 1036, Cyprus
³ Observatori de l’Ebre, CSIC – Universitat Ramon Llull, C.\Observatori 3-A, 43520 Roquetes, Spain
⁴ Departament de Matemàtiques, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain

^* Corresponding author: david.altadill.inv@gmail.com

Received: 21 May 2025
Accepted: 9 October 2025

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.