An abrupt increase of intense typhoons over the western North Pacific in early summer

Jien-Yi Tu, Chia Chou, Ping Huang, Ronghui Huang
2011 Environmental Research Letters  
The frequency and intensity of typhoons have been a focus in studying typhoon-related climate changes. In this study, we focus on a seasonal cycle of intense typhoons (category 4 and 5) over the western North Pacific, particularly changes in the number of intense typhoons in early summer. In general, 81% of intense typhoons occur in July-November (JASON), with maxima in September and October. Our analysis shows that intense typhoons have tended to occur more frequently in May since the year
more » ... since the year 2000. Before 2000, intense typhoons seldom occurred in May, with a frequency of around once per decade. After 2000, however, the frequency of intense typhoons has become much higher in May-almost once per year. We have also examined changes in the large-scale environment in the past few decades. The results show that the large-scale environment did become more favorable for intense typhoons in the 2000s, which is consistent with a larger tropical cyclone genesis index. The changes include warmer sea surface temperature, higher sea surface height, larger upper-ocean heat content, weaker vertical wind shear, increased tropospheric water vapor, and greater water vapor in the mid-troposphere. The last two might be more important than the others.
doi:10.1088/1748-9326/6/3/034013 fatcat:jnzfmy2wqfcatimpqjyodiybuq