Decadal change of Tropical Cyclone Activity over western North Pacific around late-1990s

A pronounced decadal change of tropical cyclone (TC) activity was identified over western North Pacific (WNP) around late-1990s. After late-1990s, the WNP total TC genesis number exhibited an evident decrease, particularly over southern WNP region (S-WNP: 5^oN-20^oN), which was mainly caused by reduced vorticity and descending anomalies. We also detected a significant northward migration of TC genesis from 17.2°N to 18.7°N. The above TC genesis change is attributed to the weakening of monsoon trough and local Hadley cell that is associated with sea surface temperature climate shift around the late-1990s. In terms of three prevailing TC tracks changes, the northwestward-moving track (II) became the most dominant prevailing track mode while the westward-moving track (I) became weaker, and the northeastward-recurving track (III) had a westward shift. The track shifts primarily resulted from the large-scale steering flows change, which also had played a vital role in the modulation of TC regional duration. Thus, the subtropical East Asia tended to have a higher risk of encountering TC while the Southern China had a lower risk. Additionally, a visual reduction was seen in both number and proportion of typhoons reaching categories 1 and 2, and a remarkable poleward migration was also recognized in the average latitudes where TCs have achieved their lifetime-maximum intensity.