Prof. Bin Wang

University of Hawaii, USA 

 

2pm, June 7, 2024

No. 3 Meeting Room, IAP

 

Abstract:

 Future changes in the genesis frequency and distribution of tropical cyclones (TCs) are important for society, yet uncertain. Confidence in the model projections largely relies on whether we can physically explain why the models projected such changes. The TC genesis potential index (GPI) has been extensively used to understand the large-scale processes governing climate variability and future changes in TC genesis (TCG). Whether the GPIs, derived using climatological mean data, can be applied to interpret TCG climate variations and future change is our keen concern. The relative roles of the thermodynamic versus dynamic factors in TCG also remain elusive.

        We established a Dynamic GPI (DGPI), consisting of the four circulation parameters (the 500hPa vertical motion, 850hPa absolute vorticity, vertical wind shear, and 500hPa shear vorticity of zonal winds), provides a diagnostic tool for understanding climate variation and future changes in TCG. It better represents interannual-decadal variations of TCG frequency in the western Pacific and Southern Hemisphere oceans. The results from a TC-permitting global model ascertain the four leading dynamical factors as the most influential in the present-day simulation and future projection of TCG. 

        Analysis of the CMIP6 multi-model climate simulations indicates that patterns and frequency of projected TCG are largely governed by dynamic effects—human-induced changes in atmospheric circulation, including mid-level upward motion, lower-to-mid-level cyclonic vorticity, and vertical wind shear. Conversely, the thermodynamic effect—a result of increased Maximum Potential Intensity in a warmer climate—would yield TCG patterns opposite to the model projections. Therefore, dynamic changes in response to anthropogenic greenhouse gas emissions are essential in determining the response of tropical cyclones to global warming.