Representation of Boundary-Layer Processes in Numerical Weather Prediction and Climate Models
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Representation of Boundary-Layer Processes in Numerical Weather Prediction and Climate Models John M. Edwards1 Adrian P. Lock1
· Anton C. M. Beljaars2
· Albert A. M. Holtslag3
·
Received: 26 November 2019 / Accepted: 15 May 2020 © Crown 2020
Abstract 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. Keywords Planetary boundary layer · Parametrization · Numerical weather prediction · Climate modelling
1 Introduction The modelling of the lower troposphere and its interaction with the underlying surface in numerical weather prediction (NWP) and climate models is one of the most important applications of boundary-layer meteorology. Since the first numerical forecasts were made in the middle of the twentieth century, the level of detail and sophistication of these models has continually increased, resulting in a steady increase in the accuracy of forecasts (Bauer et al. 2015). These developments would have been impossible without the sustained growth in the power and speed of digital computers that has occurred over the same period. Numerical models are continuing to develop, with the atmosphere being represented at ever-higher resolution. This increase in resolution raises a number of new modelling challenges and requires greater attention to the coupling between the planetary boundary layer (PBL) and other components of the physical system. Societal factors, such as increased urbanization and the increasing importance of air-quality forecasting, are expanding the range of
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John M. Edwards [email protected]
1
Met Office, FitzRoy Road, Exeter EX1 3PB, UK
2
European Centre for Medium Range Weather Forecasts, Reading, UK
3
Meteorology and Air Quality Section, Wageningen University, Wageningen, The Netherlands
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products required from models, as is the continuing development of Earth-system modelling for studies of climate change. An essential guiding principle in the development of numerical models has been fidelity to the underlying physics of the atmosphere. Thus, in the present context, the requirements of numerical forecasting have stimulated the development of boundary-layer meteorology, while theoretical and experimental studies have made major contributions to the success of numerical forecasting. Traditionally, the horizontal resolution of models has been much coarser than the size of energy-containing eddies in the PBL, necessitating the introduction of parametrizations to represent their net effects. There is no formal
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