Global High-Resolution Tropical Cyclone Simulations: Climate Impacts and Model Sensitivities

In an age of increasing computer power, so to comes the capability of routinely running atmospheric general circulation models (AGCMs) at increasingly high horizontal resolutions. At grid spacings of 0.5° (roughly 55 km near the equator) or finer, AGCMs have been successful at simulating tropical cyclones and are becoming the tool of choice for modeling climate impacts on tropical cyclones. Past work has demonstrated that the joint National Center for Atmospheric Research and Department of Energy Community Atmosphere Model version 5 (CAM5) has the ability to simulate tropical cyclones using idealized deterministic tests and longer-term present-day climate simulations.

First, this study explores the impact of the dynamical core on the simulation of tropical cyclone frequency, intensity and distribution in present climate. The dynamical core is often overlooked in the analysis of a global model's ability to simulate tropical cyclones. Here we compare tropical cyclone statistics in simulations with the hydrostatic finite-volume (FV) and spectral element (SE) versions of CAM5. We examine 26-year uncoupled simulations with CAM5 at 25 km using prescribed sea surface temperatures and sea-ice extent. This work indicates that the choice of dynamical core is an important source of uncertainty in modeling tropical cyclone climatology in global models.

Next, the impact of climate change on global tropical cyclone characteristics is investigated using the default CAM5-SE. Time slice experiments using the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios for greenhouse gas concentrations are evaluated and compared to present-day simulations. The CAM5-SE simulations suggest that the global number of tropical storms and hurricanes per year will decrease in a warming climate. However, there are noticeable increases in the intensity of the most intense storms. Overall, this work is part of a continued effort to understand how weather extremes may vary in a changing climate using next-generation high-resolution climate models.