Improved Simulation of Tropical Cyclone Soudelor (2015) Using a Modified Three-Dimensional Turbulence Parameterization

A modified three-dimensional turbulence parameterization scheme, implemented by replacing the conventional eddy-diffusivity formulation with the H-gradient model, has shown good performance in representing the subgrid-scale (SGS) turbulent fluxes associated with convective clouds in idealized tropical cyclone (TC) simulations. To evaluate the capability of the modified scheme in simulating real TCs, two sets of simulations of TC Soudelor (2015), one with the modified scheme and the other with the original scheme, are conducted. Comparisons with observations and coarse-grained results from large eddy simulation benchmarks demonstrate that the modified scheme improves the forecasting of the intensity and structure, as well as the SGS turbulent fluxes of Soudelor. Using the modified turbulence scheme, a TC with stronger intensity, smaller size, a shallower but stronger inflow layer, and a more intense but less inclined convective updraft is simulated. The rapid intensification process and secondary eyewall features can also be captured better by the modified scheme. By analyzing the mechanism by which turbulent transport impacts the intensity and structure of TCs, it is shown that accurately representing the turbulent transport associated with convective clouds above the planetary boundary layer helps to initiate the TC spin-up process.