## 4 Discussion  
In Event 1, occurring during 04:13 UTC, a horizontal discharge path is observed in one frame, as shown in Figures 2 and 4, and the corresponding path is detected as red, orange, and yellow dots by GLM, as shown in Figure 4. This horizontal discharge due to the optical image and horizontal trajectory by GLM can support that the image is spider lightning [14]. If so, the spider lightning can propagate below the cloud bottom. The height and total length of the horizontal propagation path recorded in the frame shown in Figure 3 are determined using a specific method, explained in Appendix A. Based on the distance of 42.5 km from the camera to the horizontal discharge, the vertical height of the path was estimated to be 634 m above sea level. The total length of the visible horizontal path, indicated by the yellow box in Figure 3, is determined to be 600 m. Due to image analysis, it was inferred that the horizontal path extended to 1.63 km. The discharge path was captured in only one frame, with the previous frame showing no propagation and the subsequent one exhibiting very bright luminosity, obscuring the path. Several subsequent frames also failed to reveal any discharge path, even though the background had less brightness, indicating that no discharge was captured. Therefore, assuming a total duration of one to two frames ranging from 40 ms to 80 ms and for the horizontal path ranging from 600 m to 1.63 km, the speed of the propagation path is determined to be between \(7.5\times 10^{3}\)-\(4.0\times 10^{4}\) m/s. This speed falls within the range reported in [39], which states that the propagation speed of positive leaders is 1.2-\(4.2\times 10^{4}\) m/s. The similarity between the estimated speed and the reported range suggests that the observed propagation path may be a positive leader. Based on this estimation, it can be hypothesized that negative charge is located at the cloud base, and the positive leader propagated horizontally beneath the cloud base. Positive leaders are characterized by lower temperature and slower speed compared to negative leaders [17; 48]. Figure 12 shows the distribution of the cluster of green and light blue dots occurring very far from the camera at the coordinates of \(25.1^{\circ}\) N-\(26.2^{\circ}\) N and \(81.5^{\circ}\) W-\(82.6^{\circ}\) W from 4.60 s to 4.94 s, with a duration of 0.330 s. This duration corresponds to the total time of the last eight frames showing the green- and blue-colored luminosity, as represented in Figure 2. As illustrated in Figure 2, the frames display a bluish bright sky during the timeframe of this cluster, with the brightness located on the right side of the image, likely corresponding to the cluster's position in the camera's field of view. If so, the average distance of the cluster of those green and light blue dots is estimated at 153 km from the camera, and the height of the discharge is estimated to be 2.28 km above sea level. When the cluster of green and light blue dots occurred, the conditions of storm, precipitation, and cloud top in the area were similar to those during the timeframe corresponding to the red, orange, and yellow dots (Figure A1a-g in Appendix B; Figure A2a-g in Appendix B). Figure 12: (**Left**) Extended coordinates of Figure 4 occurring at the coordinates of \(25.1^{\circ}\) N–\(26.2^{\circ}\) N and \(81.5^{\circ}\) W–\(82.6^{\circ}\). (**Right**) Zoomed -in view of the blue box shown in the left figure. The number of each dot represents its chronological order of occurrence. Oceanic flashes have higher optical power and energy [22], and it is plausible that the oceanic flash occurring in the area transmitted the light event from a considerable distance. Consequently, only green-blue light may have propagated through the clean air above the ocean, or the discharge may have interacted with more oxygen atoms, emitting blue and emerald-green light.