## 4 Results and Analysis  
### Relationship Between Strong Electromagnetic Pulses and Lightning Discharges  
Throughout its operational period from March to December 2023, the SY15 satellite equipped with the WEMPD has predominantly observed strong EMPs in two distinct patterns: single pulse and double pulses. On the time-frequency distribution plots, the times of arrival of varying frequencies are staggered, with the lower frequencies consistently arriving after the higher ones, creating an 'L' shaped pattern, as illustrated in Figure 3. This configuration, coupled with the pronounced dispersion traits, indicates that the signals  
Figure 3: Strong EMPs captured by the WEMPD. Panels (**a,b**) display the time-frequency distributions for the TISP and TIPP events, respectively. Panels (**c,d**) illustrate the time–frequency distributions of the aforementioned events following a dechirping process. The TISP event was located in Central Africa at coordinates (6.0349 N, 17.3659 E) and occurred at 4 August 2023 19:10:05.319101706 (LT), with \(STEC_{dec}=22.38\) TECU. The TIPP event is located in the coastal area of Colombia at coordinates (6.0349 N, 17.3659 E), and the occurrence time is 6 April 2023 05:13:12.483972000 (LT), with \(STEC_{dec}=14.15\) TECU. originate beneath the ionosphere. Consequently, the two types of signals are referred to as trans-ionospheric single pulses (TISPs) and TIPPs, respectively. The phenomenon of TIPPs was initially observed and documented by the ALEXIS satellite. Since its discovery, the underlying physics and origins of TIPPs have been extensively examined and debated. It is widely accepted that the secondary pulse within a TIPP event arises from the ground reflecting the energy of lightning discharges that occur within the cloud layer. In Figure 3, the TISP event is identified over Central Africa, specifically at coordinates (6.0349N, 17.3659E). This event was recorded at 19:10:05.319101706 on 4 August 2023 (local time, LT), with a \(STEC_{dec}\) of 22.38 TECU. On the other hand, the TIPP event is situated along the coast of Colombia, with geographical coordinates of (3.917023445N, 77.72694689W). The event took place at 05:13:12.483972000 on 6 April 2023 (LT), characterized by a \(STEC_{dec}\) of 14.15 TECU and a pulse interval of 50.23 \(\upmu\)s.  
Furthermore, as depicted in Figure 3b, alongside the dispersive TIPP event, there are also distinct horizontal wave distributions observable at frequencies of 54, 60, 61, and 67 MHz, each with bandwidths ranging from 1 to 2 MHz. These are most likely attributable to terrestrial frequency-modulation radio and television signals. The SY 15 Satellite, equipped with the WEMPD, recorded a total of 1,061 events that meet the criteria for strong EMPs. Among these, a substantial majority, specifically 78.70%, are classified as TIPP events. In contrast, the TISP events constitute a smaller proportion, precisely 21.30%, as detailed in Table 1.  
Table 1 details the synchronization of the WEMPD-detected events with those recorded by the WWLLN and the GHMLLS across different time windows. Within a narrow time window of +3 ms, the matching rate (MR) between the WEMPD and WWLLN is 9.61%. In contrast, the MR between the WEMPD and the GHMLLS is significantly lower at 1.79%, which can be primarily attributed to the fact that the detection range of the GHMLLS is confined to the immediate vicinity of the Guangdong coastline. These suggest a minimal likelihood of the WEMPD and ground-based lightning location networks detecting the same radiation source simultaneously. Expanding the timeframe to broader windows of \(\pm\)30 s, \(\pm\)150 s, and \(\pm\)300 s, the MR between the WEMPD and WWLLN increases to 90.96%, 98.49%, and 99.06%, respectively. Notably, the MR for the TIPP events achieves a perfect 100% within \(\pm\)300 s. These figures underscore a strong correlation between the WEMPD-detected events and thunderstorm lightning discharges.