# Unveiling the Core Patterns of High-Latitude Electron Density Distribution at Swarm Altitude
## 2 Data
This increased station coverage makes for improved precision in capturing the dynamics of geomagnetic disturbances by improving the accuracy of timing, intensity, and event location determination. To differentiate between low and high geomagnetic activity within the dataset, we used two SME thresholds, one set at 70 nT and the other at 230 nT, as these thresholds corresponded to the 25 th and 75 th percentiles of the cumulative distribution during the chosen period. SME values of less than 70 nT indicate periods of low geomagnetic activity at high and middle latitudes, while values greater than 230 nT identify periods of geomagnetic disturbance at these latitudes. Figure 1 illustrates the electron density (\(N_{e}\)) data that support the analysis presented in this study. Specifically, the figure displays six distinct maps arranged in two columns. The first column corresponds to the period of low geomagnetic activity (SME \(\leq\) 70 nT), while the second column represents the period of high geomagnetic activity (SME \(\geq\) 230 nT). Each column contains polar views depicting the average spatial distribution of the electron  
density during the equinox period and during the Northern Hemisphere's summer and winter solstice periods; the spring and autumn equinoxes are grouped together because electron density is subject to the same solar illumination conditions during these periods. To visualize the average polar electron density, data are plotted in a coordinate system that combines the quasi-dipole (QD) latitude and magnetic local time (MLT). The QD coordinate system introduced by [PERSON] [19] was specifically chosen due to its applicability in studying phenomena associated with horizontally stratified ionospheric currents. In order to align the data with the position of the Sun, MLT was utilized instead of QD longitude. The top of the maps correspond to noon and the bottom to midnight, and a binning grid of \(1^{\circ}\times 1^{\circ}\) is employed. Each \(1^{\circ}\) bin in MLT corresponds to a time interval of 4 min. The spatial distributions of electron density clearly show a dependence on MLT and latitude, along with variations associated with seasonality and the level of geomagnetic activity. The maps provide useful information about several well-known aspects of electron density in the high-latitude ionosphere. One notable finding is that the electron density values during the day are nearly double those during the night. The solar ionization process, which is the primary mechanism of generating free electrons in the ionosphere, is responsible for this stark contrast. Surprisingly, this characteristic remains consistent regardless of the geomagnetic activity levels, despite a clear seasonal dependence. Another notable feature is the depletion of electron density in the sub-auroral ionospheric region, particularly on the night side. This depletion is a distinguishing feature of the main ionospheric trough (MIT), which acts as a boundary between the auroral and middle latitude regions [20]. The MIT is a highly dynamic structure that serves as a signature of the magnetospheric plasmapause in the nighttime ionosphere. This characteristic remains consistent for different levels of geomagnetic activity and seasons. Finally, a notable feature that is particularly evident during equinoxes is the presence of a region with high electron density values in the mid-latitude and sub-auroral ionospheric region. It is most noticeable during periods of increased geomagnetic activity. This phenomenon is known as the storm-enhanced density (SED), and the mechanisms of its generation and decay have been studied using ground-based and space observations [21]. Panels b and d of Figure 1 show that the SED region forms a plume extending from the day side into the polar cap along the convection streamlines, giving rise to the well-known \"tongue of ionization\" (TOI). [PERSON] et al. [22] proposed that the TOI represents the ionospheric projection of the equatorial plume into the magnetosphere.