## 2 Data and Methodology
### IBI Selection Criterion  
The bubble index indicates every data point as to whether a plasma irregularity is detected. Table 1 presents the three potential cases of the bubble index [7]. Bubble index 0 (Quiet) denotes that no small-scale fluctuation is present around that data point. Bubble index 1 (Bubble) means that the data points are impacted by EPBs. Bubble index -1 means unanalyzable IBI event. According to the authors of [7], the bubble flag is related to exceeding a certain bubble probability level (e.g., \(>\)0.8 as stated in [7]). It supports additional information as to why the data point is given as the Bubble Index. In case the Bubble Index equals 0 (Quiet), the related bubble flag is also 0 (Quiet), while if the bubble index equals 1 (Bubbles exist), the related bubble flag may be either 1 (Confirmed Bubble) or 2 (Unconfirmed Bubble) [7]. In our analysis, a bubble flag of 1 (Confirmed Bubble) is chosen, which means the plasma bubble event manifests a high correlation between filtered residual magnetic field strength and filtered plasma density data. Bubble Probability can be defined as the square of the correlation coefficient (known as the coefficient of determination) because EPBs are associated with local enhancement in the magnetic field. If the bubble surpasses a specific threshold probability (e.g., \(\geq\)0.5) its bubble flag equals 1, while bubble probability is set to 0 if the bubble index is not equal to 1 or no plasma density data exist around the magnetically detected events (Unconfirmed Bubble). This is because users may set \begin{table}
\begin{tabular}{c c} \hline \hline
**Bubble Index** & **Description** \\ \hline
0 & Quiet \\ \hline
1 & Bubble \\ \hline –1 & Unanalyzable \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The Bubble index criterion. an accurate standard on the relationship between filtered residual strength and filtered plasma density by merging the bubble probability and the bubble index. For our selection of IBI events, we chose events with bubble index equal to 1, bubble flag equal to 1, and bubble probability \(\geq\)0.5 and subsequently checked their corresponding \(n_{e}\) irregularities. Figure 1 is a typical example of a Swarm L2-IBI event. The IBI index and the IBI probability are plotted in solid black and dashed red lines, respectively. The blue line represents the \(n_{e}\) profile along the path of the Swarm B satellite. The event has an IBI index equal to 1 and IBI probability closer to 0.91 as shown in Figure 1, in addition to a bubble flag equal to 1 not shown in Figure 1. These three conditions confirm the existence of a plasma bubble event. We can recognize intense irregularities in the \(n_{e}\) profile between (08:12-08:15 UT) during the same time of the occurrence of the plasma bubble event. In the present study, we examined seven years of Swarm L2-IBI observations (2014-2020) during geomagnetic storms. We have divided the geomagnetic storms according to [57] into three categories. Moderate storm (\(-50\) nT \(>\) Dst \(>-100\) nT), intense storm (\(-100\) nT \(>\) Dst \(>-200\) nT), and super storm (\(-200\) nT \(>\) Dst \(>-350\) nT). Table 2 introduces the geomagnetic storms along with their corresponding Dst index values. The hourly Dst index values are obtained from OMNI data ([[https://omniweb.gsfc.nasa.gov/form/dx1.html](https://omniweb.gsfc.nasa.gov/form/dx1.html)]([https://omniweb.gsfc.nasa.gov/form/dx1.html](https://omniweb.gsfc.nasa.gov/form/dx1.html)) (10 January 2020)). The driver of the geomagnetic storm is obtained from the space weather website ([[https://spaceweather.com/archive.php](https://spaceweather.com/archive.php)]([https://spaceweather.com/archive.php](https://spaceweather.com/archive.php)) (20 February 2021)). The driver of the storm could be a Coronal Mass Ejection (CME), a Co-rotating Interaction Region (CIR), a stream of solar wind, or the Interplanetary Magnetic Field turning southward (- IMF Bz). According to Table 2, we have two super storms, seven intense storms, and fifty moderate storms.