Impact of Three-Dimensional Turbulent Transport Parameterization on Numerical Prediction of Tropical Cyclones

Turbulent transport processes in the inner core of tropical cyclones (TCs) have unique characteristics. At the local mixing scale, turbulence eddies generated by the boundary layer processes and cloud processes are inter-connected three-dimensional turbulent mixing with comparable magnitudes in the vertical and horizontal due to the large lateral contrast across the eyewall and rainbands. The turbulence induced lateral entrainment of dry moat air into the convective clouds serves as an important mechanism for the generation of turbulent kinetic energy (TKE) in the eyewall and rainbands via lateral entrainment instability. At the TC vortex scale, as the turbulent radial inflow approaches the radius of maximum wind, the boundary layer becomes ill-defined as the air is pulled up into the active eyewall convection. While the concept of the boundary layer may still be applicable in the eyewall and rainbands. Due to the intense turbulence in the eyewall, the turbulence can extend beyond the boundary layer, which plays a vital role in TC intensity changes.

To advance our understanding of how three-dimensional turbulent mixing in the TC inner core affects TC intensification and to evaluate the impact of parameterizing turbulent mixing in three-dimensional on operational numerical prediction of TCs, we use the Hurricane Analysis and Forecast System (HAFS) with a newly implemented scale-aware three-dimensional TKE turbulence scheme to simulate TCs of 2022 – 2023 hurricane seasons in the north Atlantic and eastern Pacific basins. We compared the simulated storm track, intensity, and structure with the National Hurricane Center best-track and aircraft observations. Promising results are shown of using the three-dimensional scheme to represent the turbulent mixing in the TC inner core for both major and weak hurricanes including TSs. Comprehensive analyses on individual cases, such as Hurricane Otis (2023), have also been performed to understand how turbulent mixing in the TC inner core affects the pathway to the storm rapid intensification.