Publications by Andrew Dawson


Reliable low precision simulations in land surface models

CLIMATE DYNAMICS 51 (2018) 2657-2666

A Dawson, PD Dueben, DA MacLeod, TN Palmer


Forcing Single-Column Models Using High-Resolution Model Simulations.

Journal of advances in modeling earth systems 10 (2018) 1833-1857

HM Christensen, A Dawson, CE Holloway, CE Holloway

To use single-column models (SCMs) as a research tool for parameterization development and process studies, the SCM must be supplied with realistic initial profiles, forcing fields, and boundary conditions. We propose a new technique for deriving these required profiles, motivated by the increase in number and scale of high-resolution convection-permitting simulations. We suggest that these high-resolution simulations be coarse grained to the required resolution of an SCM, and thereby be used as a proxy for the true atmosphere. This paper describes the implementation of such a technique. We test the proposed methodology using high-resolution data from the UK Met Office's Unified Model, with a resolution of 4 km, covering a large tropical domain. These data are coarse grained and used to drive the European Centre for Medium-Range Weather Forecast's Integrated Forecasting System (IFS) SCM. The proposed method is evaluated by deriving IFS SCM forcing profiles from a consistent T639 IFS simulation. The SCM simulations track the global model, indicating a consistency between the estimated forcing fields and the true dynamical forcing in the global model. We demonstrate the benefits of selecting SCM forcing profiles from across a large domain, namely, robust statistics, and the ability to test the SCM over a range of boundary conditions. We also compare driving the SCM with the coarse-grained data set to driving it using the European Centre for Medium-Range Weather Forecast operational analysis. We conclude by highlighting the importance of understanding biases in the high-resolution data set and suggest that our approach be used in combination with observationally derived forcing data sets.


rpe v5: an emulator for reduced floating-point precision in large numerical simulations

GEOSCIENTIFIC MODEL DEVELOPMENT 10 (2017) 2221-2230

A Dawson, PD Duben


A study of reduced numerical precision to make superparameterization more competitive using a hardware emulator in the OpenIFS model

JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 9 (2017) 566-584

PD Duben, A Subramanian, A Dawson, TN Palmer


An approach to secure weather and climate models against hardware faults

JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 9 (2017) 501-513

PD Duben, A Dawson


Windspharm: A High-Level Library for Global Wind Field Computations Using Spherical Harmonics

Journal of Open Research Software Ubiquity Press, Ltd. 4 (2016)

A Dawson


eofs: A Library for EOF Analysis of Meteorological, Oceanographic, and Climate Data

Journal of Open Research Software Ubiquity Press, Ltd. 4 (2016)


Simulating weather regimes: impact of model resolution and stochastic parameterization

Climate Dynamics 44 (2015) 2177-2193

A Dawson, TN Palmer

© 2014, Springer-Verlag Berlin Heidelberg. The simulation of quasi-persistent regime structures in an atmospheric model with horizontal resolution typical of the Intergovernmental Panel on Climate Change fifth assessment report simulations, is shown to be unrealistic. A higher resolution configuration of the same model, with horizontal resolution typical of that used in operational numerical weather prediction, is able to simulate these regime structures realistically. The spatial patterns of the simulated regimes are remarkably accurate at high resolution. A model configuration at intermediate resolution shows a marked improvement over the low-resolution configuration, particularly in terms of the temporal characteristics of the regimes, but does not produce a simulation as accurate as the very-high-resolution configuration. It is demonstrated that the simulation of regimes can be significantly improved, even at low resolution, by the introduction of a stochastic physics scheme. At low resolution the stochastic physics scheme drastically improves both the spatial and temporal aspects of the regimes simulation. These results highlight the importance of small-scale processes on large-scale climate variability, and indicate that although simulating variability at small scales is a necessity, it may not be necessary to represent the small-scales accurately, or even explicitly, in order to improve the simulation of large-scale climate. It is argued that these results could have important implications for improving both global climate simulations, and the ability of high-resolution limited-area models, forced by low-resolution global models, to reliably simulate regional climate change signals.


Simulating weather regimes: impact of model resolution and stochastic parameterization

CLIMATE DYNAMICS 44 (2015) 2177-2193

A Dawson, TN Palmer


Importance of oceanic resolution and mean state on the extra-tropical response to El Niño in a matrix of coupled models

Climate Dynamics 41 (2013) 1439-1452

A Dawson, AJ Matthews, DP Stevens, MJ Roberts, PL Vidale

The extra-tropical response to El Niño in configurations of a coupled model with increased horizontal resolution in the oceanic component is shown to be more realistic than in configurations with a low resolution oceanic component. This general conclusion is independent of the atmospheric resolution. Resolving small-scale processes in the ocean produces a more realistic oceanic mean state, with a reduced cold tongue bias, which in turn allows the atmospheric model component to be forced more realistically. A realistic atmospheric basic state is critical in order to represent Rossby wave propagation in response to El Niño, and hence the extra-tropical response to El Niño. Through the use of high and low resolution configurations of the forced atmospheric-only model component we show that, in isolation, atmospheric resolution does not significantly affect the simulation of the extra-tropical response to El Niño. It is demonstrated, through perturbations to the SST forcing of the atmospheric model component, that biases in the climatological SST field typical of coupled model configurations with low oceanic resolution can account for the erroneous atmospheric basic state seen in these coupled model configurations. These results highlight the importance of resolving small-scale oceanic processes in producing a realistic large-scale mean climate in coupled models, and suggest that it might may be possible to "squeeze out" valuable extra performance from coupled models through increases to oceanic resolution alone. © 2012 Springer-Verlag.


Simulating regime structures in weather and climate prediction models

Geophysical Research Letters 39 (2012) L21805

A Dawson, TN Palmer, S Corti


Rossby wave dynamics of the North Pacific extra-tropical response to El Niño: Importance of the basic state in coupled GCMs

Climate Dynamics 37 (2011) 391-405

A Dawson, AJ Matthews, DP Stevens