## 3 Results and Discussion  
The possible plasma bubble occurrences for selected geomagnetically disturbed days, whose Dst index (Dst \(<-100\) nT) falls in the category of strong geomagnetic storms under the ascending phase of Solar cycle 25, are investigated using the sTEC depletion characteristics. Based on the above criteria, only four storm days, namely 27 February, 23 and 24 March and 23 April 2023 (referring to three geomagnetic storm events), are chosen for analysis in this study [80]. Figure 3 presents the variation of interplanetary and geomagnetic indices (IMF Bz, Dst, ap, and Kp) for the chosen storm days. All selected days show a high Kp value (Kp \(>\) 5) with an increased ap (ap \(>\) 90 nT) except for April 23 which presents the highest ap index (ap = 56 nT). [PERSON] et al. [81] showed that some days with ap \(<\)50 nT showed strong ionospheric irregularities. The Dst is also reported to be less than \(-100\) nT on all days, suggesting strong geomagnetic storms [82]. April 23 recorded the lowest Dst (\(-165\) nT) of all the disturbed days. Earlier research showed an increase in the occurrence probability of EPBs with magnetic activity wherein the main phase of the storm coincides with the local dusk time, thereby uplifting the F layer plasma through penetrating eastward electric fields and facilitating the RTI development [54; 83]. However, some studies revealed the magnetic activity inhibiting the occurrence of the EPBs in the presence of disturbance dynamo electric fields (DDEFs) and westward electric fields, forcing the F layer electron density downward [58; 84]. It can be marked that the IMF Bz variance is higher (22 nT) on 23 April than on the other days, suggesting that a sudden change in its polarity can manipulate the equatorial electric fields for triggering the pre-reversal enhancement (PRE) scenario that seeds the formation of EPBs [42; 85]. The extreme values of all the geomagnetic indices for the storm days are given in Table 2.  
The \(\sigma_{\varphi}\), S4, and sTEC for all the available constellations of the storm day, the preceding day, and the successive day for the three storm events (27 February, 23, 24 March, and 23 April) are presented in Figures 4-6, respectively. We observe a severe scintillation activity in terms of high S4 and \(\sigma_{\varphi}\) on the 23 March and 23 April 2023 storm days. It is also evident that during all the storm days, the pre- and post-storm periods presented high scintillation activity in terms of S4 and \(\sigma_{\varphi}\) except for the 24 March and 23 April post-storm periods. Although there is a high geomagnetic activity observed in all the storm days (see Figure 4), the scintillation activity is suppressed in the 27 February and 24 March (Figures 5 and 6) storm days compared to pre- and post-storm periods. The possible reasons for the suppression of the scintillation are due to the reduction in the F layer height due to westward prompt penetration or the disturbance dynamo electric fields (PPEFs/DDEFs) reducing the PRE which is responsible for the possible plasma bubble manifestation and thereby enhancing the scintillation activity. The role of PPEF or DDEF during the geomagnetic storm to trigger/suppress EPBs by manipulating the zonal electric field is summarized in the earlier literature [7]. Figure 4: The \(\sigma_{\varphi}\) (**top panel**), S4 (**middle panel**) and sTEC (**bottom panel**) from all the available constellations on the days before the storm (25 and 26 February), during the storm (27 February), and after the storm (28 February) in 2023. The red dashed line shows the local sunset terminator for the above days. Figure 3: The IMF Bz, Dst, ap and Kp values for the storm days of 27 February, 23 and 24 March, and 23 April during the year 2023 from top to bottom. Figure 5: The \(\sigma_{\varphi}\) **(top panel)**, S4 **(middle panel)** and sTEC **(bottom panel)** from all the available constellations on the days before the storm (22 March), during the storm (23, 24 March) and after the storm (25 March) in 2023.