# Unveiling the Core Patterns of High-Latitude Electron Density Distribution at Swarm Altitude
## 5 Discussion
Without  
Figure 7: Polar view of the III and IV fundamental modes obtained from the MEMD of electron density distribution during the equinoctial (first row), summer (second row), and winter (third row) periods under high geomagnetic activity in the Northern Hemisphere. SuperDARN polar potential maps obtained using the statistical convection model CS10 are superimposed on each mode as level curves. Maps are represented in the QD–magnetic latitude (MLat) and MLT reference system. The concentric circles are plotted in 10\({}^{\circ}\) intervals, with the outermost circle corresponding to 50\({}^{\circ}\). direct solar radiation, electrons in the ionospheric plasma tend to recombine with ions, leading to a decrease in electron density within the F-layer throughout the nighttime. Furthermore, ionospheric wind movements and diffusion processes can influence electron distribution, adding to the day-night asymmetry. These factors contribute to the creation of plasma flows that shift electron density across different regions of the ionosphere during various phases of the day and night. It is interesting to note that there is a difference in the day-night asymmetry of the electron distribution between the summer and winter seasons. During the summer there is generally higher ionization of the upper atmosphere due to more direct and prolonged solar incidence, resulting in a higher electron density in the F-region during daylight hours. As a result, the amplitude of the day-night asymmetry may be greater in the summer than in the winter. This is precisely what is observed when comparing the results obtained for this fourth mode in summer and winter. However, it is important to note that the day-night asymmetry depends on other factors as well, such as the latitude, solar activity, and presence of geomagnetic events. In this study, we fixed the level of solar activity while analyzing two levels of geomagnetic activity. When examining the characteristics of the fourth mode during high geomagnetic activity across different seasons, as shown in the maps in the right column of Figure 7, it can be seen that the day-night asymmetry follows the same seasonal patterns, with only the intensity level varying. Overall, it can be concluded that the fourth mode, obtained through the decomposition of the different datasets, is the result of a combination of factors including interaction with the solar radiation, the nighttime electron recombination process, and ionospheric wind movements. These processes play a dominant role compared to the other modes, as the fourth mode is the most energetic one. While the analysis of the convection cell structure makes no significant contribution to a better understanding of the electron density distribution in the fourth mode, it is critical to comprehend the third mode. The third mode is presented in Figures 6 and 7 (left columns) in relation to the season and the level of geomagnetic activity. During periods of high geomagnetic activity, the third mode exhibits a region of high electron density at high latitudes on the day side. This characteristic is consistent throughout the year. This region corresponds to the cusp, which is a distinct area within the day side auroral oval near noon. The cusp is known for enhanced ion and electron precipitation, and is considered the primary location for the transport of magnetosheath plasma into the ionosphere. It typically appears as a single spot that spans a few hours of MLT, and its position is influenced by the \(B_{y}\) and \(B_{z}\) components of the IMF. However, it is important to note that the cusp does not always manifest as a single structure. In certain cases, especially when the IMF \(B_{y}\) component is large or when there are changes in IMF orientation, the cusp can bifurcate into two or more distinct regions. This bifurcation phenomenon adds complexity to the cusp structure, and highlights the dynamic nature of the interaction between the solar wind and Earth's magnetosphere.