Dynamically-Derived Tropical Cyclone Intensity Changes over the Western North Pacific

Study of the impact of global warming on tropical cyclone (TC) intensity is subject to uncertainty in historical datasets, especially in the western North Pacific (WNP) basin, where conflicting results have been found with the TC datasets archived in different organizations. In this study the basin-wide TC intensity in the WNP basin is derived dynamically with a TC intensity model, based on the track data from the Joint Typhoon Warning Center (JTWC), the Regional Specialized Meteorological Center (RSMC) of Tokyo, and the Shanghai Typhoon Institute (STI) of China Meteorological Administration, respectively. The dynamically-derived TC intensity is compared to the three datasets and used to investigate trends in TC intensity. The associated contributions of changes in SST, vertical wind shear and prevailing tracks are also examined. The evolution of the basin-wide TC intensity in the JTWC best track dataset can be generally reproduced over the period 1975-2007. Dynamically-derived data based on the JTWC, RSMC, and STI track datasets all show an increasing trend in the peak intensity and the frequency of intense typhoons, mainly due to the combined effect of changes in SST and vertical wind shear. This study suggests that the increasing intensity trend in the JTWC dataset is real, but may be overestimated. On the other hand, the TC intensity trends in the RSMC and STI intensity datasets are dynamically inconsistent. Numerical simulations also suggest that the frequency of intense typhoons is more sensitive to changes in SST and vertical wind shear than the peak and average intensities defined in previous studies.