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climate modelling


Weathering change: playing the long game


Beth Harlen reports on the strides being made within


the UK climate modelling community


M


ore than 20 years ago in the UK ‘there was a very conscious choice to make a large long-term investment in climate science. Tis


accelerated the development of climate models,’ according to Pier Luigi Vidale[1]


, professor at


the University of Reading, UK, and National Centre for Atmospheric Science (NCAS) senior scientist. Vidale says this investment, along with the attention the UK government has devoted to environmental problems and the efforts it has made to engage the scientific community, is largely why ‘the UK now leads the way in climate modelling’. One such investment was made in 1990 with the opening of the Met Office Hadley Centre, a world-leading research centre for climate science. Te dynamics group at the centre, now led by Nigel Wood, is responsible for the development of the ‘dynamical core’ of UK weather and climate models – that is, the scheme that solves the equations of atmospheric motion. Recently, ‘EndGame’, an improved version of the dynamical core of the UK’s ‘Unified Model’ has been completed and adopted operationally. Tis is set to have a significant impact on the simulation of atmospheric flow. Development of EndGame began nine years


ago and, says Vidale, it was nearly terminated as a project because the community had overly optimistic expectations in terms of when the next generation of dynamical cores would be available. ‘EndGame was viewed very much as a less important interim solution, but, through sheer force of will, the group continued down that path,’ said Vidale. On paper, the scheme the group proposed was more expensive than the next generation was expected to be – but, because of the capabilities of the latest supercomputers and substantially larger size of the problems currently being addressed, the gain made in scaling and turnaround has proven to


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be far superior – not to mention the fact that the next-gen models are still roughly a decade away from completion. ‘To be honest,’ Vidale continued, ‘no one


was expecting the scalability of the model based on EndGame to be this good, and it turned out that the new dynamical core is ideal for taking advantage of the latest generation of supercomputers.’ Te stability of the scheme enables the application to run on a supercomputer for extended periods without the need to restart the model – a common problem


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in the past, as the chaotic nature of the equations being solved can lead to ‘bad numbers’ (NaNs) that essentially cause the application to fail. Because the new model’s dynamical core


is less damping, it will enable Vidale’s High- Resolution Global Climate Modelling group to simulate more energetic storms with their global climate models, with a standard mesh size of 25km. In 2012, the group was able to simulate category-three hurricanes (which are classified in terms of wind speed from one to five, with five being the most extreme) and a few of the


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