Future Changes in the Western North Pacific Tropical Cyclone Activity Projected by a Multi-Decadal Simulation with a 16-km Global Atmospheric GCM

How tropical cyclone activity in the northwestern Pacific might change in a future climate is assessed using multi-decadal AMIP-style and time-slice simulations with the ECMWF Integrated Forecast System (IFS) at 16-km global resolution. The model reproduces many aspects of the present-day typhoon climatology and variability well, including the full intensity distribution and genesis locations, and their changes in response to El Niño and the Southern Oscillation.

The 16-km IFS projects a small change in the typhoon frequency at the end of the 21st century related to a distinct southward shift in the genesis locations. It is likely driven by the southeastward penetration of the monsoon trough/subtropical high circulation system and the southward shift in the activity of the synoptic-scale tropical disturbances in response to the strengthening of deep convective activity over the central equatorial Pacific in a future climate.

The 16-km IFS also projects about fifty percent increase in the power dissipation index mainly due to a significant increase in the frequency of the more intense storms, which is found to be comparable to the natural variability in the model. Based on the composite analysis of large samples of super-typhoons, both the development rate and the peak intensities of these storms increase in a future climate, which is consistent with their tendency to develop more to the south and within an environment that is thermodynamically more favorable for faster development and higher intensities and dynamically virtually unchanged. Coherent changes in the vertical structure of the super-typhoon composites show system-scale amplification of the primary and secondary circulations with the signs of contraction, including an upward shift in the frequency of the intense updrafts and overall stronger convection in the eyewall.