## 2 Data and Methods
### EPB Detection Based on LP Measurements of Plasma Density  
To automatically detect EPBs, we devised and developed an algorithm based on in situ LP measurements, which works as follows. For each orbit, we consider the timeseries of theplasma density measurements \(n_{s}\) from LP (\(s=e\) for electron density measurements by CSES-01 and \(s=i\) for ion density measurements by Swarm B) and compute the density baseline according to the following equation:  
\[\widetilde{n}_{s}(t_{k})=\frac{1}{57}\sum_{j=k-28}^{k+28}n_{s}(t_{k}), \tag{1}\]  
where \(k\) denotes the \(k\)th point of the timeseries. We use a running mean with a window size larger than the maximum expected size of an equatorial ionospheric irregularity(see e.g., [54]). Specifically, given the temporal resolution of our datasets (see Section 2.1), this corresponds to taking a running mean with a window size of 57 points, corresponding to \(\sim\)170 s or 1200 km (transformed using the average orbital velocity of CSES-01 and Swarm B, i.e., 7.2 km/s). We then take the density ratio with respect to the baseline \(\delta n_{s}=n_{s}(t_{k})/\tilde{n}_{s}(t_{k})\) and, in order for a given interval to contain a plasma depletion, we impose the following conditions:  
1. The ratio \(\delta n_{s}\) between the density measured at each point along the semiorbit and the running mean of the density is less than 1/2;
2. The above condition is satisfied for at least five points along the semiorbit;
3. Points whose time distance is lower than 40 s are considered as belonging to the same depletion; otherwise, they are considered as belonging to two (or more) different depletions. 4. Identified intervals are located in a latitudinal band from \(-30^{\circ}\) to \(30^{\circ}\) of quasi dipole magnetic latitude [55]. The first condition allows identifying any abrupt density decrease along the orbit. Since we are interested in detecting EPBs, whose density is significantly reduced compared with the background (see, e.g., [38; 56] and references therein), we define a plasma depletion as a region where the plasma density is less than half that of the surrounding plasma. This condition also agrees with [57], who, in order to automatically detect polar cap patches (see, e.g., [58]) using ion density data from LP onboard Swarm satellites, imposes that the ratio between the foreground density and the background density is greater than 2. This threshold guarantees to consider irregularities whose density gradient is able to disturb HF radio propagation and degrade GNSS signals (see, e.g., [59]). For this reason, we extend this definition also to ionospheric irregularities in equatorial regions. The second condition ensures that the detected density decreases are not due to any sporadic fluctuations. The minimum interval length has been chosen based on visual inspection of several orbits, resulting in a good compromise between excluding random fluctuations while concurrently being able to identify scale irregularities on the order of tens of kilometers. Imposing a time difference greater than 40 s between two consecutive detected intervals containing depletions allows for a better estimation of the number of plasma depletions detected along the orbit. Such a condition, indeed, ensures to correctly count multiple plasma depletions that eventually occur along a semiorbit, also evaluating whether plasma fragmentation occurs inside a plasma bubble. Such an interval has been chosen based on visual inspection of several orbits as the best trade-off between the possibility of considering fragmentation of large structures and of maintaining information about the nature of the detected irregularity. The last condition allows for investigating only depletions occurring at low latitudes. All imposed thresholds reduce the number of false positive detections to less than 10%, the latter being mainly linked to the inability of the moving average to follow the density profile in cases of failure of the LP data acquisition.