Seasonal to decadal variations of tropical cyclone genesis in Northwestern Pacific in recent three decades

Tropical cyclones mostly originate the northwestern Pacific (NWP), which have great significance on global and regional climate changes.However, many documents mainly have focused on the changes of tropical cyclone in NWP with little spatial locations, and their methods are descriptive statistics.Thus, this paper uses the nearest neighbor hierarchical clustering method to gather the tropical cyclone genesis regions in NWP during the period of 1981 to 2010.Main results are summarized as follows.(1) Northern South China Sea, east of the Philippine islands and near the Mariana islands are three high frequent occurrence regions.(2) Cyclones mostly occur in summer and autumn, especially in July to September, and their spatial distribution widely ranges from 5N to 40N.A few cyclones generate in spring and summer, locating at south of 10N.(3) Tropical cyclones in El Nio are fewer than in La Nia years.Annual numbers of tropical cyclones are obviously different before and after 1995.The annual frequency in the period of 1981~1995 is higher than the period of 1996~2010.In addition, in the later period, the locations of tropical cyclones migrate northeasterly.