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

Wednesday, 17 December 2014
Haozhe He1,2, Jing Yang1, Rui Mao1, Yuqing Wang3 and Daoyi Gong1, (1)Beijing Normal University, State Key Laboratory of Earth Surface Processes and Resource Ecology (ESPRE), Beijing, China, (2)Beijing Normal University, Academy of Disaster Reduction and Emergency Management Ministry of Civil Affairs & Ministry of Education, Beijing, China, (3)University of Hawaii at Manoa, International Pacific Research Center and Department of Meteorology, School of Ocean and Earth Science and Technology, Honolulu, HI, United States
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: 5oN-20oN), 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.