Tropical cyclones in a two-way global-to-regional nested weather-climate model

Global weather-climate models can skillfully reproduce the observed number and interannual variability in tropical cyclones but cannot replicate the observed intensity of storms (Zhao et al 2009). Multi-decadal simulations were performed using a two-way nested version of the Geophysical Fluid Dynamics Laboratory's (GFDL) High Resolution Atmosphere Model (HiRAM), a global model forced with observed SSTs. Nested simulations, with grid-cell-widths of 40 km and 25 km on their nested grids, were compared with uniform-resolution global grids of 110 and 50 km, to demonstrate the potential for nested simulations to improve tropical cyclone climatologies.

Nested-grid simulations over the Western Pacific and over the North Atlantic show a larger proportion of tropical cyclones reaching maximum wind speeds above 40 m/s compared to the uniform-resolution simulations, an intensity distribution closer to that in observations. All of the simulations have roughly the same number of TCs in both basins, except for the 110 km uniform-resolution simulation; for this simulation using a nested grid brings the TC count closer to that in the other simulations. Interannual variability, spatial distribution, and the annual cycle of TCs will also be examined in the nested simulations.