Tropical Cyclone Simulations: The Impact of Model Top/Damping Layer and the Role of Stratospheric Gravity Waves

This paper investigates the impact of model top and damping layer on the numerical simulation of tropical cyclones (TCs) and reveals the significant role of stratospheric gravity waves (SGWs). TCs can generate SGWs, which propagate upward and outward into the stratosphere. These SGWs can reach the damping layer which is a consequence of the numerical scheme employed, where they can affect the tangential circulation through the dragging and forcing processes. In models with a higher top boundary, this tangential circulation develops far from the TC and has minimal direct impact on TC intensity. By comparison, in models with a lower top (e.g., 20 km), damping layer is located just above the top of the TC. The SGW dragging in the damping layer and the consequent tangential force can thus induce ascent outside the eyewall, promote latent heat release, tilt the eyewall, and enlarge the inner-core radius. This process will reduce inner-core vorticity advection within the boundary layer, and eventually inhibits the intensification of the TC. This suggests that when the thickness of the damping layer is 5 km, TC numerical model top height should be at least higher than 20 km to generate more accurate simulations.