## 4 Summary and Conclusions  
In this study, the sTEC depletion characteristics are investigated during the geomagnetic storm days (Dst \(<-100\) nT) in the ascending phase of Solar cycle 25 to ascertain possible triggering or suppression of the EPBs. Following the criterion for detecting the presence of EPBs from the corresponding sTEC depletion characteristics, such as depletion depth \(\Delta\)(sTEC), apparent duration (t\({}_{\rm sTEC}\)), and maximum values around the depletion, we confirm that out of the three storm events considered in this study, only one event (23 April 2023) is associated with an enhanced EPBs, whereas, during the rest of the events, the regular EPBs are notably suppressed. The storm events on 27 February as well as 23 and 24 March in 2023 report inhibited TEC depletion, confirming suppressed EPBs during the period that is supported by subdued S4 (0 to 0.48) and \(\sigma_{\varphi}\) (0.01 to 0.59) indices. However, the observations on 23 April 2023 confirm that all GNSS constellations witness sTEC depletions between 15:00 UT and 18:00 UT, which is in good agreement with the recorded scintillation indices (S4 and \(\sigma_{\varphi}\)). The ROTI variations at locations ranging from near equatorial latitude to the outer edge of the EIA crest latitudes in the same longitude sector corroborate the prevailing irregularities due to EPBs above the region. In brief, the characteristic depletion depths (22 to 45 TECU) and depletion times (28 to 48 min) across different constellations confirm the triggering of EPBs during the geomagnetic storm event on 23 April 2023. We argue the possible enhanced dusk time pre-reversal enhancement (PRE) is the cause for the instability observed in the sTEC magnitudes. Moreover, 23 April 2023 witnessed moderate-to-strong scintillations across signals from all constellations as per the classification scheme based on the scintillation indices. The signals from GPS show the largest depletion of \(\sim\)48 TECU within an apparent duration of 45 min, whereas that of Galileo present the least depletion depth of \(\sim\)22 TECU with an apparent duration of 40 min. Although the signals from the BeiDou constellation have the smallest duration of 22 min, they evidence repeated depletions during the observed span, confirming relatively more vulnerability to the storm onset. We perform an analysis of the equivalent ionospheric delay to realize the consequences of TEC depletions in respective frequencies of the GNSS constellations that confirms the maximum delay (\(\sim\)13.09 m) in GPS L5, whereas the minimum delay (3.56 m) is seen in Galileo L1. Similarly, the maximum S4 is observed in the GPS constellation, while the largest \(\sigma_{\varphi}\) is observed in the BeiDou constellation in all three frequencies. In brief, the present objective attempts to strengthen the relation between sTEC depletion and scintillation indices observed through a high-rate GISTM receiver; both effects are the consequences of the development of EPBs at the equatorial and low-latitude regions. The future assignment of this work is to include a greater number of geomagnetic storms as they occur for substantiating the hypothesis adopted in this study. An established relationship between TEC depletion and EPBs could pave the way for employing the most abundant traditional geodetic GNSS receivers established under IGS and UNAVCO along with other regional and individual stations to participate in understanding and modeling the sTEC depletions associated with EPBs and developing regional as well as global scintillation mitigation strategies. In addition, the opportunity of multi-constellation signal availability opens a doorway for maneuvering the adaptation of interoperability among signals to enhance the performance of satellite-based navigation, positioning and timing solutions under intense ionospheric scintillations.