## 3 Results
### Case 8 (2 June 2016)  
On 2 June 2016, geomagnetic conditions were quiet (minimum Dst \(\sim-4\) nT; daily SSN:14). At approximately 03:40 UT, the Roquetes Digisonde detected RSF ionogram signatures along with oblique traces propagating southeastward, as depicted in Figure 9a. In contrast, the Dourbes ionosphere only showed satellite traces (STs), a weak TID signature noted in ionograms [45], and there was no indication of SF. To better understand the irregularity features, we analyzed SF-associated MSTID signatures using a GNSS d-TEC map (Figure 9b), which revealed MSTID presence exclusively over Roquetes. Given the RSF observed over Roquetes, we examined the ROTI fluctuations in the region. As shown in Figure 9c, a significant ROTI fluctuation of -0.3 TECU/min was recorded over Roquetes with an nmF2 of 352 km.  
To identify potential signatures of topside ionospheric irregularities, we analyzed the latitude Ne profiles of Swarm A and C satellites (Figure 9d-f), over Roquetes around 03:42 UT. The Ne profile of Swarm C (Figure 9e) exhibited a fluctuation southward of Roquetes between latitudes of 35-40\({}^{\circ}\) N, indicating the potential influence of RSF develop  
Figure 9: (**a**) SF event was observed over Roquetes at 03:40 UT and Dourbes was encountered by STs; (**b**) MSTID signatures in GPS d-TEC map (pink markers indicate locations of Dourbes and Roquetes); (**c**) ROTI fluctuations observed over Dourbes and Roquetes (pink markers); (**d**) Swarm A–C track over Dourbes and Roquetes; and (**e**) latitude Ne and (**f**) dNe profiles of Swarm A–C over Dourbes and Roquetes latitude.  
ment over Roquetes. However, no notable topside irregularity signatures were observed over Dourbes. Figure 9f illustrates a significant dNe fluctuation of \(\sim\)0.5 \(\times\) 10\({}^{4}\) elec/cm\({}^{3}\) near Roquetes, confirming the coexistence of topside irregularities with the RSF.  
This case stands out as unique because, unlike previous cases where SF signatures were more prevalent at higher midlatitude stations, here, we observed RSF at the lower midlatitude station (Roquetes) without corresponding irregularity signatures at the higher midlatitude stations. Generally, midlatitude irregularity distributions are influenced by equatorward-propagating disturbances originating from the MIT, facilitated by MSTID wavefronts [18; 46]. However, in this case, RSF was recorded at Roquetes even in the absence of irregularities at northern latitudes.  
This inconsistency suggests two possible scenarios: the RSF development could be attributed to locally generated irregularities [30] or the irregularity densities transported from the equatorial ionosphere. Previous studies, such as [PERSON] et al. 2003 [50], have documented the coexistence of plasma bubbles and blobs with RSF signatures over the equatorial ionosphere. Their research, supported by Swarm Ne measurements, confirmed the simultaneous occurrence of topside and bottomside irregularities in the equatorial region. Similarly, [PERSON] et al. 2020 [39] reported strong correlations between ground-based ionospheric observations and Swarm Ne, highlighting similar local time statistical trends. [PERSON] et al. 2016 [34] also noted significant fluctuations in Ne using 2 Hz Swarm LP measurements, corroborated by JULIA radar data from the Jicamarca equatorial observatory.  
However, the association of RSF with topside ionospheric irregularities over midlatitude regions remains underreported. While this case provides evidence of RSF coexisting with topside irregularity structures in the latitude Ne profile of Swarm over Roquetes, the fluctuation observed in the Ne profile is not sufficiently pronounced to conclusively support the case.