## 3 Results
### Swarm Satellite Electron Density Data  
On 4 August 2020, Swarm-B passed near the explosion site at approximately 18:57 UT, heading toward the North Pole. The satellite trajectory is represented by a red line projected onto a geographical map, as shown in Figure 2. Swarm-B required approximately 30 min to traverse its path, starting from the initial point in the Southern Hemisphere at 18:57 UT and reaching the final point in the Northern Hemisphere at 19:21 UT. Specifically, the trajectory of the satellite was projected along the 24.5\({}^{\circ}\) magnetic meridian located 8\({}^{\circ}\) west of the explosion site. The explosion site is indicated with a dotted magenta symbol on the map. The traced magnetic field lines (green and blue lines) connecting the conjugated hemispheric points in the two different regions are shown in green and blue, with the initial tracing points in the Southern Hemisphere marked as 1 and 2, respectively. The endpoints of these field lines at 300 km altitude represent the conjugate hemispheric points. Figure 1: The solar wind parameters and the geomagnetic activity indices. **(a)** The polar cap north index, **(b)** interplanetary north–south magnetic field component (IMF-Bz), **(c)** solar wind speed, **(d)** solar wind pressure, and **(e)** SYMH index on 4 August 2020. The vertical dashed line indicates the Beirut port explosion on 15:08 UT. The green and blue traced magnetic field lines represent the conjugate perturbations in the observed electron density and magnetic field data recorded by Swarm-B along its trajectory, respectively. The black horizontal arrows indicate the latitudinal endpoints of the traced magnetic field line (green). The ionospheric electron density observed along the path of the Swarm-B satellite, as shown in Figure 2b, demonstrates disturbances in the ionospheric density in the Northern Hemisphere, extending across a wide latitudinal range (30-60\({}^{\circ}\)N). In contrast, ionospheric density disturbances were also observed along the satellite's path in the Southern Hemisphere, but were more localised, spanning a narrower latitude range (30-40\({}^{\circ}\)S) than that in the Northern Hemisphere. At the geomagnetic equator, the two equatorial ionospheric crests (north and south) appear asymmetric, but remain undisturbed. The first-time derivatives and residual electron densities presented in Figure 2c illustrate the exact latitudinal locations of the hemispheric perturbations. Specifically, the electron density was subtracted from a cubic spline function fitted to a 10 s interval. The 10 s interval was chosen through experimentation with the data to achieve a good location of transient variation. As a result, the residual data shown in Figure 2c represent spatial disturbances occurring at scales smaller than approximately 74 km (calculated as 10 \(\times\) 7.4 km/s), where 7.4 km/s is the average velocity of the Swarm-B satellite. The first two quiet days, according to the GFZ Helmholtz Centre for Geosciences ([[https://kp.gfz.de/en/data](https://kp.gfz.de/en/data)]([https://kp.gfz.de/en/data](https://kp.gfz.de/en/data)); accessed on 20 April 2024), representing the quietest days of the event month (9 and 10 August 2020) within the 15:00-19:30 UT period, were also investigated. Figure S4 in the Supplementary Materials shows that both paths exhibited clear Ne disturbances in both the Northern Hemisphere near Beirut Port and at its conjugate point in the Southern Hemisphere. These two quiet  
Figure 2: **(a)** Geographic map showing the trajectory of Swarm-B (red line) on 4 August 2020, during the period 18:57-19:30 UT, near the explosion region. Dot in magenta colour indicates the position of Beirut port. **(b)** Electron density data retrieved from Swarm-B during its passage near the explosion site (18:57–19:30 UT) shown in blue, with cubic spline fitting represented by the red solid line. **(c)** The first-time derivative of the electron density (blue) and the residuals (difference between the data and the fitted curve) shown in red.