The Budget of Turbulence Kinetic Energy (TKE) in a Large-Eddy Simulation of a Tropical Cyclone

Turbulence Kinetic Energy (TKE) is a commonly used measure of turbulence intensity. It is defined as the kinetic energy associated with eddies (i.e., fluctuations) in a turbulent flow. In many disciplines, it is common to base Planetary Boundary Layer (PBL) parameterizations on a predictive equation for TKE, which often neglects terms presumed to be small to reduce computing requirements for real-time weather prediction; however, some terms may not be negligible in tropical cyclones, where horizontal gradients of winds can be comparable to vertical gradients. To gain insight, we have been analyzing budgets of TKE in large-eddy simulations of idealized hurricanes. A simulation of a small but intense hurricane with 31-m horizontal grid spacing will be used for this talk. Our analysis focuses on three dynamically different regions of the hurricane: the inflowing boundary layer, where the TKE budget is simplest; the corner-flow region in the eyewall, where radial gradients play a large role in the TKE budget; and the eyewall above the boundary layer, where the role of buoyancy has been controversial. Based on these results, recommendations are made for changes to TKE-based PBL parameterizations in weather-prediction models.