Representation of Boundary-Layer Processes in Numerical Weather Prediction and Climate Models

Boundary-layer schemes are essential components of numerical weather-forecasting and climate models. From simple beginnings 50 years ago, they have grown in sophistication and detail. Here, we review development and discuss the key processes to be represented and how they have most commonly been parametrized. We conclude by discussing the challenges posed by ever-increasing model resolution and a growing emphasis on the forecasting of extreme events. Throughout, we emphasize the place of the boundary-layer scheme within the whole model and its interactions with other components of the model.