3.1. TC genesis and onset
Fig. 2 shows the TC genesis locations relative to the position
of the TC domain over the KP (28Ne40N,
120E138E) and changes in the TC onset time during
summer (JuneeAugust) and fall (SeptembereNovember)
seasons throughout 1966 to 2009. In this study, the TC genesis
locations and the time of TC occurrence are based on the first
TC location and time data provided by the RSMC Tokyo-
Typhoon Center. It was found that there were more TCs
(191 TCs) during the summer season in the northwestern region
(average: 15.9N, 139.5E) than during the fall season
(136 TCs, average: 14.5N, 143.2E), and that this difference
was statistically significant at the 90% confidence level. The
summer TCs tended to occur late in the summer season,
whereas many of the fall TCs occurred relatively early in the
fall season; this is reflected in the right sided onset distribution
for summer (mean onset time: July 31st) and the left sided
onset distribution for fall (mean onset time: September 25th).
The trend analysis results showed that the TC onset time has
become faster than in the past, but not statistically significant
for both the summer and fall TCs at the 90% confidence level.