The T-REX valley wind model intercomparison project

This paper presents key results from the T-REX valley wind model intercomparison project. The objective of this project is to compare the effects of model dynamical cores and physical parameterizations on the simulation of thermally-forced slope and valley winds. The intercomparison makes use of a suite of 2D and 3D simulations to explore: i) the significance of varying the dynamical core including the parameterization of turbulence and mixing, ii) the uncertainties associated with the parameterization of radiation transfer and surface-atmosphere interactions. The setup consists of an idealized valley-plain topography and an atmosphere initially at rest. The simulations run from sunrise to sunset and include uncoupled and coupled model versions, i.e. model runs with specified surface heat fluxes and more realistic runs where the surface heating is determined by the interaction of the radiation transfer scheme, the land surface scheme, and the simulated flow field. The following questions will be addressed: What are the reasons for model differences in simulated slope and valley flows, stratification of the valley atmosphere, boundary layer height, and valley wind strength? How do the simulations differ with respect to integral diagnostics such as along-valley flux and vertical heat exchange, versus more local diagnostics such as wind speeds and boundary layer evolution?