## 1 Introduction
The Rate of TEC Index (ROTI) is a GNSS-based parameter that quantifies the extent of amplitude and phase fluctuations in GNSS radio signals, reflecting the dynamics and spatial distribution of ionospheric irregularities. While ROTI has been widely studied, especially in equatorial and high-latitude regions, a limited number of studies focused on midlatitude regions (e.g., [20; 21]). Midlatitude ionospheric irregularities are typically formed by lower electron density in these regions (e.g., [22; 23]). In a recent study, [PERSON] et al. 2024 [23] found a correlation between ROTI and RSF activity over European Digisonde stations during a period of low to moderate solar activity in 2011. Their results indicated that RSF events often coincided with higher ROTI values (>0.15 TECU/min), suggesting that GWs or polarization electric fields act as drivers for RSF development at midlatitudes. In recent years, numerous Low-Earth-Orbit (LEO) missions operated at altitudes between 400 and 1000 km. These LEO satellites (e.g., SWARM) provide global coverage, facilitating the characterization of ionospheric irregularities across various orbital altitudes [24]. The middle-latitude irregularities [25] in the topside ionosphere may primarily result from plasmaspheric ambipolar diffusion and equatorward neutral wind-driven plasma drift along geomagnetic field lines. While previous studies (e.g., [26; 27]) have investigated midlatitude irregularity characteristics, the properties of irregularities within this structure remain unclear. Swarm, a polar-orbiting satellite constellation, has collected in situ Ne and topside TEC data for over nine years, providing insights into global ionospheric irregularities and corresponding scintillations across different times, latitudes, and solar activity levels. Observations by [PERSON] et al. 2010 [28] using CHAMP (altitude \(\sim\)400 km) and KOMPSAT-1 (\(\sim\)685 km) showed that midlatitude plasma density fluctuations exhibit a hemispheric asymmetry. [PERSON] et al. 2020 [29] found that midlatitude MSTID occurrence in the northern and southern hemispheres anticorrelates with declining solar activity after midnight, while Swarm (\(\sim\)450-500 km) exhibited more frequent winter hemisphere irregularities under low solar activity. Based on an \(\alpha\)-Chapman model with variable scale height, [PERSON] et al. 2022 [30] estimated effective scale height values, revealing diurnal variations with maximum values appearing at \(\sim\)450 km in the early morning and evening, with complex altitude-dependent behaviour during the day. Recent work (e.g., [31]) identified MSTIDs through satellite Langmuir Probe (LP) Ne observations during the September 2017 storm. [PERSON] et al. 2021 [32] characterized plasma bubbles (Ionospheric Bubble Index, IBI) during geomagnetic storms, noting that notable IBI values appear at lower altitudes for moderate storms, with higher-altitude IBI (Swarm-B) increasing as storm intensity rises. Topside irregularities have also been investigated using the rate of change of density (ROD) and the density index (RODI) derived from 2 Hz LP measurements on Swarm satellites. [PERSON] et al. 2019 [33] developed indices--ROD, RODI, and a large-scale Ne gradient--from Swarm data to represent small-, medium-, and large-scale irregularities, which are sensitive to meso- and large-scale irregularities. Studies by [PERSON] et al. 2016 [34] reported high seasonal and longitudinal pattern correlation between topside ionospheric irregularities using ROTI and RODI indices. [PERSON] et al. 2020 [35] compared Swarm in situ observations with ground-based amplitude scintillation events from GPS-SCINDA in Africa, particularly for Swarm A and C, which orbit at lower altitudes. [PERSON] et al. 2020 [36] documented global ionospheric irregularities, identifying three key regions but without a specific focus on midlatitude topside irregularities.