## 4 Results
### Analysis of Ionospheric Data from Ionosonde  
Several recent papers investigated the co-seismic (and post-seismic) effects on the ionosphere, which are much documented and modelled (e.g., [73]). By combining data from Doppler sounding systems, ionosondes, and GNSS receivers, [PERSON] et al. [8] distinguish various types of disturbances variations, following the Turkey mainshock, which propagate around the F-region peak at different velocities and through different mechanisms. [74] identified two large-scale travelling ionospheric disturbances (LSTIDs) over Turkey, with phase speeds of 534 and 305 m/s, following the second major EQ at 10:24 UT on 6 February 2023. These disturbances suggest that strong earthquakes can perturb equatorial ionospheric currents, including the E-region equatorial electrojet (EEJ) and F-region ionospheric radial current (IRC). [PERSON] et al. [75] analysed the TEC data and found that the amplitude of the ionospheric response caused by the daytime M7.5 EQ exceeded by five times that caused by the nighttime M7.8 main EQ. Significant anomalies in TEC data were also found [76]. Seventeen minutes after the mainshock, a Doppler ionosonde detected a co- or post-seismic disturbance over a 3010 km radio path from Kuwait to the Institute of Ionosphere in Almaty [77]. Acoustic waves at a height of 232 km in the ionosphere appeared 568 s after the Rayleigh surface wave reached the sub-ionospheric point, matching the predicted time for vertically moving acoustic waves. This disturbance lasted 160 s with a significant amplitude above 2 Hz, exceeding normal Doppler frequency fluctuations [8]. Most of the above results were about the co-seismic effects on the ionosphere. In any case, they encourage us to investigate, also in search of pre-seismic effects. Our multi-instrument approach allows for a comprehensive analysis of how the preparation phase of seismic events impacts the ionosphere, providing a clearer understanding of the resulting disturbances. The Nicosia (Cyprus) ionosonde data are then analysed to find ionospheric variations possibly linked to the Turkey EQs in the 90 days preceding the first major EQ. The ionospheric station of Nicosia is indeed located inside the EQ preparation zone according to the formula by [63] (see R[km] in Table 1). Figure 19: Swarm Alpha (**a**) and Bravo (**b**) (from left to right panels): electron density data with respect to geomagnetic latitude; first differences (NeAD method for Ne data); electron temperature data with respect to geomagnetic latitude; plasma potential data with respect to geomagnetic latitude; and map with the location of the epicentre of the earthquake (green star), Dobrovolsky area (yellow circle), and analysed track (red line) for 15 December 2022 (i.e., 53 days before the earthquake). Coloured square indicates the anomaly automatically detected by NeAD. The application of the ionosonde multiparametric method imposes some constraints to three ionospheric parameters. The method revealed a single anomaly occurred about 78 days before the Turkey EQs. While analysing the characteristics of the F2 layer, the authors stated [75] that they did not find any anomaly, also because they analysed a shorter interval. The time variations of the three ionospheric parameters are shown by Figure 20. Such an anomaly occurred on November 20, 2022 at 06:00 UT, i.e., 77.84/78.20 days before the two EQs (Table 2). Since the anomaly (Figure 20) occurred in a day with the geomagnetic index Ap = 5 nT, the criterion (Ap \(\leq\) 15 nT) was strictly satisfied. The values of the auroral electrojet index AE have also been checked in the previous 6 h, verifying the low level of the auroral activity, which could reach middle latitudes and perturb foF2.