An Open-Source, Physics-Based, Tropical Cyclone Downscaling Model with Intensity-Dependent Steering

Abstract: An open-source, physics-based tropical cyclone downscaling model is developed, in order to generate a large climatology of tropical cyclones. The model is composed of three primary components: (1) a random seeding process that determines genesis, (2) an intensity-dependent beta-advection model that determines the track, and (3) a non-linear differential equation set that determines the intensification rate. The model is entirely forced by the large-scale environment. Downscaling ERA5 reanalysis data shows that the model is generally able to reproduce observed tropical cyclone climatology, such as the global seasonal cycle, genesis locations, track density, and lifetime maximum intensity distributions. Inter-annual variability in tropical cyclone count and power-dissipation is also well captured, on both basin-wide and global scales. Regional tropical cyclone hazard estimated by this model is also analyzed using return period maps and curves. In particular, the model is able to reasonably capture the observed return period curves of landfall intensity in various sub-basins around the globe. The incorporation of an intensity-dependent steering flow is shown to lead to regionally dependent changes in power dissipation and return periods. Advantages and disadvantages of this model, compared to other downscaling models, are also discussed.