## 2 Materials and Methods
All 4 window sizes are used to obtain the detrended TEC curves as shown in Figure 1 (upper panels). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**S.No.**} & **GNSS Constellation (RINEX Symbols)** & \multicolumn{2}{c}{**Available Frequencies (GHz) for Scintillation Indices**} & \multicolumn{2}{c}{**Signal Combinations for TEC**} \\ \cline{2-5}  & **Constellation** & **Signal 1** & **Signal 2** & **Signal 3** & \\ \hline
1 & GPS (G) & L1 (1.57) & L2 (1.22) & L5 (1.17) & L1P-L2P \\ \hline
2 & GLONASS (R) & L1 (1.60) & L2 (1.24) & NA & L1 CA-L2 CA \\ \hline
3 & Galileo (E) & E1 (1.57) & E5a (1.17) & E5b (1.20) & E1-E5a \\ \hline
4 & BeiDou (C) & B1 (1.56) & B3 (1.26) & B2 (1.20) & B1-B2 \\ \hline
5 & GAGAN (S) & L1 (1.57) & NA & L5 (1.17) & L1 CA-L5 \\ \hline
6 & IRNSS/NavIC (I) & NA & NA & L5 (1.17) & NA \\ \hline \end{tabular}
\end{table} 
Table 1: The available frequencies and signal combinations used in the PolaRx5S receiver monitoring unit established at KL University, Guntur, India for scintillation indices and TEC retrievals under different GNSS constellations. \begin{table}
\begin{tabular}{c l c c c c} \hline \hline
**S. No** & **Geomagnetic Indices** & **27 February 2023** & **23 March 2023** & **24 March 2023** & **23 April 2023** \\ \hline
1 & IMF Bz (nT) & 6.7 & 0.3 & 4.6 & 21.7 \\
2 & Dst (nT) & \(-132\) & \(-126\) & \(-156\) & \(-165\) \\
3 & ap (nT) & 94 & 94 & 94 & 56 \\
4 & Kp & 6.7 & 7 & 8 & 8.3 \\ \hline \end{tabular}
\end{table} 
Table 2: The extreme values for the geomagnetic indices (IMF Bz, Dst, ap, and Kp) for the strong storm days in the ascending phase of the 25 th solar cycle. To ensure that the depletion is due to plasma bubbles and not because of ionospheric shift perturbations or any bias in the data, we impose thresholds on the depletion curve characteristics [14]. The TEC depletion depth \(\Delta\)(sTEC) \(\geq\) 10 TECU, the apparent duration (t\({}_{\text{sTEC}}\)) of the depletion should be 10 < t\({}_{\text{sTEC}}\) < 180 min, the absolute minimum of the TEC depletion should be \(\geq\)5 TECU, and the maximum value of detrended TEC across the left and right side of the depletion \(\geq\)5 TECU. \(\Delta\)(sTEC) is defined as the difference between the minimum value of the detrended TEC curve and the mean of the maximum left and right of the depletion value. The t\({}_{\text{sTEC}}\) is the time taken by the depletion depth and is the difference between the times of maximum value on the right and left of the depletion. To demonstrate the retrieval of TEC depletion parameters through employing different moving average window sizes, we show the sTEC, its moving average and detrended sTEC for a specimen GNSS signal (PRN 32 of GPS and PRN 89 of Galileo constellations) in Figure 1. From our observations, it is realized that the 60 min window size is the most suitable candidate for inferring the TEC depletion characteristics coping with the plasma bubble criteria. The 10 min window size underfits the TEC detrended curve, with shallow TEC depletions that relate to the medium-scale travelling ionospheric disturbances (MSTIDS) and lower atmospheric gravity waves [77; 78]. The 90 min and 120 min window sizes overfit the data and include some of the depletions with more values of depletion depth and depletion duration from the plasma bubble criteria. The window size with the 60 min moving average is best suited for both shorter and longer plasma bubble operations. In Figure 2 (upper panel), we show the sTEC (black line) for PRN 32 of GPS and PRN 89 of Galileo constellations along with the 60 min moving average (blue line) and their detrended TEC (red line with marker 'x'). The zoomed-in version of respective depletions (red line with marker 'x') indicating the calculation of depletion depth (\(\Delta\)(sTEC)) and its apparent duration (t\({}_{\text{sTEC}}\)) is presented in Figure 2 (lower panel). A zero line (dark grey) is drawn in this figure to differentiate the positive and negative values in the detrended TEC curve.