## 3 Results and Discussion
The red dashed line shows the local sunset terminator for the above days. Figure 6: The \(\sigma_{\varphi}\)**(top panel)**, S4 **(middle panel)** and sTEC **(bottom panel)** from all the available constellations on the days before the storm (21, 22 April), during the storm (23 April), and after the storm (24 April) in 2023. The red dashed line shows the local sunset terminator for the above days. To identify the PRNs affected by significant depletions and thereby meet the criteria for their association with EPBs, we concentrate on the regular occurrence duration of EPBs (15:00 UT to 18:00 UT) for all storm events. From Figure 7, it can be seen that the TEC depletions (red color) meet the plasma bubble criteria only on 23 April 2023. On the other hand, the rest of the geomagnetic storm events (27 February, 24 March) hardly evidence any noticeable TEC depletion (grey color), inferring that the regular post-sunet EPBs were suppressed during these periods owing to the disagreement of electrodynamics for manifesting a PRE at the evening terminator. The TEC value is additionally reduced by processes such as the rapid nighttime recombination of the F-layer followed by density re-distribution. These two processes result in shallow TEC slopes and lack the recovery section; however, they both were removed from our TEC depletion statistics as they do not satisfy the association criteria for the presence of EPBs. Although there are TEC depletions (blue color) observed on 23 March 2023, they hardly meet the thresholds set for EPBs and may rather incur noises due to gravity waves, neutral wind shear, medium-scale travel ionospheric disturbances (MSTIDs), etc. Figure 8 depicts the ionospheric piercing points (IPP) at each time of the observed satellites above the receiver location during the geomagnetic storm event on 23 April 2023 determining the localization characteristics of EPBs corresponding to GNSS-observed scintillation indices. The color bar in each plot (left and right) indicates the intensities for the S4 and \(\sigma_{\varphi}\), respectively. The shaded points represent the IPP positions with no significant scintillation intensity. The red and green line shows the location of the magnetic equator and the approximate equatorial ionization crest anomaly (EIA) location. We note that lower threshold limits are considered for the respective S4 and \(\sigma_{\varphi}\) index plots to eliminate the presence of noises which are irrevement to the scintillation phenomena. In Figure 9, we analyze the ROTI variation on 23 April 2023 geomagnetic storm day at the present location (KLEF) and that obtained from SIMuRG for other geodetic GNSS stations under the IGS network (IISC, HYDE, and LCK3), ranging from near equatorial latitude to outer edge of equatorial ionization anomaly (EIA) crest latitude. The results confirm the prevailing TEC irregularities confined to the EIA region, substantiating the connection between TEC depletion at the location and prevailing EPBs over the Indian longitude sector. Figure 7: The observed sTEC for all the available GNSS constellations (GPS, GLOMASS, Galileo, BeiDou) with depletion depths \(\Delta\)(sTEC) \(<\) 5 TECU (grey), \(5\leq\Delta\)(sTEC) \(<\) 10 TECU (blue), and \(\Delta\)(sTEC) \(\geq\) 10 TECU (red) during the four geomagnetic storm days considered in this study. The results are in good agreement with the earlier review of EPBs in the global equatorial and low-latitude region indicating the latitudinal extent of bubbles of approximately \(\pm 15^{\circ}\) geomagnetic latitudes [7]. Figure 8: Geographic map of India showing the location of the GISTM receiver and EPBs overhead from the recorded scatter points of S4 (**left**) and \(\sigma\varphi\) (**right**) indices at ionospheric piercing points (IPPs; gray color). The color bars indicate the level of the scintillation indices. The approximate locations of magnetic equator and EIA crest are shown in red and green color contours, respectively.