Potential based Thermodynamics with Consistent Conservative Cascade Transport for Implicit Large Eddy Simulation: PTerodaC³TILES version 1.0

Abstract. A new computational fluid dynamics code for Large-Eddy Simulation (LES) of the atmospheric boundary layer and convection is presented and made available. A key novelty is that moist thermodynamics is formulated in terms of thermodynamic potentials, ensuring thermodynamic consistency. Despite the apparent complexity of the thermodynamic potential approach, the model's performance demonstrates that it is feasible and effective at reasonable computational cost for three-dimensional simulations. Semi-implicit semi-Lagrangian numerical methods are used; such methods are unusual for simulating boundary layer and convective flows and are more typical of global atmospheric models. Moreover, the model includes no explicit scheme to represent subgrid-scale fluxes of scalars and momentum but relies instead on the mixing and dissipation resulting from the numerical methods used; in other words, it employs Implicit LES (ILES). Sample results from several standard LES test cases show that the model's ability to capture the main aspects of the flows is comparable to other LES models. At the same time, the results highlight limitations of the ILES approach near the bottom boundary and suggest that ILES might need to be augmented in some way, for example, by distributing the convergence of surface fluxes over several model layers. Also, results for a marine stratocumulus case show a significant sensitivity to different options for the numerical methods and parameters used. Further development and application of the code would benefit from a deeper understanding of both the bottom boundary behaviour and the sensitivities to numerics.