## 1 Introduction  
While [PERSON]'s theory depicts the ionosphere as a stratified layer, observations and studies have demonstrated the presence of electron density (Ne) irregularities. These irregularities can occur at various altitudes and across all latitudes, ranging in size from a few centimetres to several hundred kilometres [1]. Detecting and analyzing these plasma density irregularities is challenging due to their complex origin, driven by numerous factors such as space weather events and diurnal or seasonal ionization variations. The midlatitude ionosphere is generally less affected by irregularities compared to the equatorial and polar regions. These irregularities are predominantly characterized by diffused plasma structures, known as midlatitude spread F (SF), which can persist from several minutes to a few hours (e.g., [2, 3, 4, 5, 6]). SF events are typically classified into two types based on the spread echo patterns seen in ionograms [7]. Range SF (RSF) appears in the lower frequency segments (<2-2.5 MHz) of F-region traces, where echoes are diffused and extend over 10 km or more beyond the main trace. Alternatively, frequency SF (FSF) occurs when diffused echoes concentrate near the critical frequency of the F trace. [PERSON] 1991 [3] suggested that range spreading results from the frontal structure of large-scale irregularities spanning approximately 1000 km, whereas frequency spreading is caused by scattered echoes from ionospheric structures near the zenith. [PERSON] and [PERSON] 1991 [8] identified the Perkins instability as a candidate mechanism driving midlatitude SF. [PERSON] 1973 [9] originally proposed that variations in the eastward electric field or southward wind could destabilize plasma equilibrium in the midlatitude ionosphere, leading to the formation of plasma instability structures. However, the Perkins instability has a relatively slow growth rate (\(\sim\)10\({}^{-4}\) s\({}^{-1}\)) [10], making it insufficient to fully account for midlatitude SF formation. This growth rate can be significantly amplified by gravity waves (GWs) and associated electric field perturbations near the bottomside ionosphere [11]. [PERSON] et al. 1994 [12] highlighted the importance of GWs in enhancing the instability, although this is limited by higher-order nonlinear effects. [PERSON] 1996 [13] observed that midlatitude SF occurrence is anticorrelated with solar flux, which is linked to changes in Upper Atmospheric Neutral Particle Density (UA-NPD) that influence the amplitude of medium-scale travelling ionospheric disturbances (MSTIDs). The link between UA-NPD and MSTID amplitude [14] explains the observed anticorrelation between midlatitude SF occurrence and UA-NPD. Numerous studies have analyzed MSTIDs using total electron content (TEC) data from GNSS receivers (e.g., [15; 16; 17]). [PERSON] et al. 2023 [18] highlighted the role of MSTIDs as a dominant seeding mechanism for SF at midlatitudes, correlating MSTID activity with SF over eight European Digisonde stations based on 2017 GNSS-detrended TEC maps. [PERSON] et al. 2018 [19] observed midlatitude F-region plasma density irregularities associated with Es-layer irregularities over Arecibo during geomagnetically quiet periods, capturing detailed dynamics and wavelike variations in the F-layer peak. The data revealed pronounced instabilities with significant upwelling of plasma density into the topside ionosphere. Numerical simulations have explained many key features observed in the midlatitude ionosphere, such as patchy Es layers, MSTIDs, and bottomside and topside irregularities. These simulations underscore the role of GWs. These GWs contribute to the generation and structure of Es layers, drive dynamo-induced MSTIDs, and excite currents in the F region, leading to bottomside irregularities. Electric fields induced by GWs in the E region are mapped along magnetic field lines into the topside ionosphere, generating irregularities through convection and advection [19].