## 3 Results
At first glance, the occurrences of spread F were indeed quite high during this period of interest. Especially at the three lower latitude stations of TO536, YG431, and OK426, we notice that the scattered echo traces are mainly SSF, as shown in Figure 4. It seems that the lower the latitude of the station is, the earlier the time of SSF appears. On the top panel (WK545) in Figure 4, the SSF that occurred at 17-19 UT (02-04 JST) is not as strong as spread F at the three lower latitude stations. At 20-21 UT, the types of spread F changed to weak FSF. The different morphology of spread F traces suggested that the generation mechanism of spread F at WK545 may be different from that at other stations. In addition, Figure 4 also presents the high-frequency occurrence of sporadic E (Es) with a relatively small magnitude at altitudes of \(\sim\)100 km. Intriguingly, the so-called cusp type Es, which is connected to the thick E layer trace [29], developed well in the ionospheric E region after 21 UT (06 JST) during the local morning. To uncover the possible difference in the occurrence and characteristics of spread F before and after the storm onset, we first investigate the ionosonde observations on 15 July 2003. Since the occurrence of spread F on 15 July was preferentially concentrated at 12-18 UT (21-03 JST) as shown in Figure 3, the period 11-16 UT (20-01 JST) was selected to show the evolution of spread F. The observed spread F was mainly FSF in Figure 5 during the period 11-16 UT on 15 July. We note that satellite traces, appearing as one or more quasi replicas of the F layer trace [47; 48; 49], are clearly seen from 12 UT to 16 UT at To536. In other subgraphs of Figure 4, for example, clear satellite traces can be seen near the second hop at 15 UT (24 JST) at WK545, YG431, and OK426. [PERSON] [49] and [PERSON] et al. [50] also observed the satellite trace near the second hop. Interestingly, some of the observed morphology of FSF, for example at 12 UT (21 JST) at OK426, was similar to the daytime spread F observed by [PERSON] et al. [47]. In addition, we note that flat type Es can be seen in almost every ionogram, showing a wide distribution of Es over Japan on 15 July. It should be mentioned that the existence of Es may affect the observation of the ionospheric F region to some extent. As a comparison with Figure 5, we represent the development of spread F in Figure 6 during the same UT period, but on 16 July, when the magnetic storm occurred, to further study the possible difference. The echo traces in Figure 6 show that the occurrence of spread F is obviously reduced and mostly replaced by the normal F region trace. At the lowest latitude station of OK426, spread F started to be FSF at 14 UT, then developed into SSF at 15-16 UT. At the highest latitude station of WK545, the type of spread F during the period 14-16 UT is MSF, accompanied by obvious satellite traces. In Figure 6, flat type Es can still be identified, but the magnitude is weaker than that observed in Figure 5. The results from Figures 4-6 suggest that the occurrence time and type of spread F caused by storms are significantly different from those generated during non-storm periods. It also suggests that the generation mechanism should be somewhat different. Figure 4: Development of spread F at (top panel) W5545, (second panel) TOS56, (third panel) YC431, and (bottom panel) OK426 during 17–22 UT (02-07) ST) on 16 July 2003. Coordinate reference information is given in the lower left figure. Figure 5: Development of spread F at (**top panel**) WK545, (**second panel**) TOS36, (**third panel**) YG431, and (**bottom panel**) OK426 during 11-16 UT (20-01 ST) on 15 July 2003. Coordinate reference information is given in the lower left figure, ordinate reference information is given in the lower left figure. Figure 6: Development of spread F at (**top panel**) WK545, (**second panel**) TOS36, (**third panel**) YG431, and (**bottom panel**) OK426 during 11–16 UT (20-01 JST) on 16 July 2003. Coordinate reference information is given in the lower left figure.