The T-REX valley wind model intercomparison project: Lessons learned

This paper presents key results and lessons learned from the T-REX valley wind model intercomparison project. The objective of the intercomparison project was to compare the effects of model dynamical cores and physical parameterizations on the simulation of thermally driven slope and valley winds. The setup consisted of an idealized valley-plain topography and an atmosphere initially at rest. The simulations were run with full (dry) physics including a radiation transfer, land surface, and turbulence scheme from sunrise to sunset. We found that the temporal evolution of the valley-mean up-valley wind is similar for all models, except due to differences in timing. For the spatial structure significant differences are found among the models, especially with regard to the vertical structure of the boundary layers. For the bulk flow evolution, the largest source of differences among the models is related to the parameterization of the soil-surface-atmosphere interaction and the radiation transfer scheme, while for the vertical structure of the flow the turbulence parameterizations have a strong influence. The paper is complemented by a discussion of practical issues encountered during the model intercomparison and recommendations for future model intercomparisons of thermally driven flows.