## 3 Results
### COSMIC Satellite RO-Electron Density Data  
On 4 August 2024, the four COSMIC satellites generated 3000 RO profiles worldwide. The initial points of each trajectory are marked with red dots on the global map shown in Figure 7a. To examine conjugate ionosphere disturbances related to the event, only full trajectories within 10-60\({}^{\circ}\)E longitude, \(\pm\)40\({}^{\circ}\) latitude, and the 15:00-16:00 UT time window were selected, as highlighted by the green box. Figure 7b shows that only five trajectories were selected based on the criteria mentioned earlier. The trajectories were projected onto the world map as red lines, with their universal time marked at the start of each path. All the selected paths were recorded at approximately 15:30 UT (15.5 h), approximately 22 min after the Beirut explosion (15:08 UT). For clarity in the analysis and comparison, the paths  
Figure 6: **(a)** The DMSP-F17 trajectory projected onto the geographic map, shown in red, with blue and green lines representing the International Geomagnetic Reference Field-traced magnetic field lines connecting conjugate hemispheric points. **(b)** The raw ion density (N\({}_{\rm i}\)) in blue and its cubic spline fit in red. **(c)** The first-time derivative of ion density (blue) and the residuals (difference between the observed data and cubic spline fit) in red. were numbered arbitrarily based on their archived order. The most significant trajectories in this study were 2635, 2634, and 362. * Trajectories 2635 and 362 are expected to be located at conjugate hemispheric points;
* Trajectory 2634 lies near the dip equator and was deliberately selected to determine whether the observed perturbation was due to the mapped field line or transient variations from the travelling ionospheric disturbances. Fortunately, this configuration of the COSMIC satellite constellation provides a valuable opportunity to capture the prompt response of conjugate hemispheric regions to the explosion. Similar to Swarm-B and DMSP-F17, the ionospheric disturbances were identified using the first-time derivative of the RO data and by subtracting the cubic spline fit from the original RO data to obtain the residual. Figure 8 presents an analysis of the three trajectories:  
* 2635 at UT = 15.6 h (top row);
* 2634 at UT = 15.53 h (middle row);
* 362 at UT = 15.55 h (bottom row). The left column (Figure 8a-c) displays the geographic locations of the trajectories. The middle column (Figure 8d-f) shows the RO electron density (blue) with a cubic spline fit (red). The right column (Figure 8g-i) presents the first-time derivative (blue) and residual (red). Both the residual and first-time derivative reveal clear signatures of ionospheric disturbances at higher altitudes in trajectories 2635 and 362 (top and bottom rows, respectively). However, trajectory 2634, located over the dip equator, showed no disturbances, despite its close timing to trajectory 2635. The presence of electron density perturbations in trajectories 2635 and 362 motivated us to trace the magnetic field lines between them. It  
Figure 7: (**a**) A geographic map of the initial location of each COSMIC path retrieved on 4 August 2020, marked in red dots. (**b**) The paths of COSMIC satellites within 1500–1600 UT. The path number and the universal time of each path are marked next to the start of each trajectory path. is also worth noting that we investigated the COSMIC-RO profiles near Beirut Port and its conjugate location during the quietest days (9 and 10 August 2020) between 15:00 and 16:00 UT, as well as during the hour preceding the event, as shown in Figures S1 and S2 of the Supplementary Materials. All profiles from quiet days and hours preceding the event exhibited minimal perturbation. Figure 9 illustrates the mapping of the IGRF magnetic field lines connecting the Northern and Southern Hemispheres. The red lines represent the COSMIC RO trajectories, with their corresponding universal times labelled in red. The blue lines indicate the traced magnetic-field lines.