Next-generation weather model development with the Met Office
07 Feb 2017
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The weather might just be the UK's favourite topic of conversation – probably in part because it is so difficult to predict what it will do next. But making the weather more predictable is precisely what we’re trying to do.

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​​​​​Credit: STFC

 

​The Met Office is the UK’s national weather service and underpins all our prediction capabilities, from short and long-term weather forecasts to climate change. At the heart of the Met Office’s weather forecasting is a computational model, which takes the current and past state of the weather and simulates how it will evolve over the next few hours, days and months.

As you’ve already guessed, this modelling program isn’t as simple as an app on your phone; in fact, it requires a supercomputer – but even supercomputers are constantly evolving and improving, at a similar speed to our own personal devices. While the number of transistors being packed onto a chip is increasing, however, energy restrictions mean that increases to processor clock speed have ground to a halt.

“Instead, manufacturers are using the additional transistors to produce chips containing more than one processor core,” says Hartree Centre computational scientist Rupert Ford. “It is now down to the software to make use of these additional cores to achieve higher performance.”

Supercomputers which might once have had just a handful of processor cores now routinely contain hundreds of thousands of them.

“Harnessing a vast number of cores to do something as complex as a weather forecast is no mean feat,” says Rupert. “An analogy that is often used is ploughing a field: it is much easier to get two large horses to pull a plough than it would be to use 1,000 chickens!

When you introduce different types of computer processor, it may be even more complex – say, 500 chickens and 5,000 mice, which must be programmed in different ways. Given that the large, complex models used by organisations like the Met Office typically take 10-15 years to develop and have an operational life of approx. 30 years, this presents a big challenge - how to write a program for a computer that does not yet exist?”

This is the basis of the GungHo project, a collaboration between the Met Office, Natural Environment Research Council (NERC) and the Hartree Centre. We are working to develop the next generation weather and climate computer model, due to become operational in the mid-2020s. The name of the code generation tool is PSyclone, and it is hoped that it will be extended for use in other domains in future.

The construction of such a model requires expertise in both meteorology and computational science - which presents another challenge, as few scientists are experts in both. A key design principle adopted within the GungHo project is therefore the 'separation of concerns' where elements of the software dealing with the natural science are kept apart from those dealing with the computational science (i.e. what type of supercomputer the model is running on).

“One of the most novel aspects of the project is that those parts of the model that adapt performance to suit the supercomputer it is running on, are automatically generated,” says Andrew Porter, another of the scientists working on the project.

“This removes the need for programmers to hand-code software for a specific supercomputer, greatly improving productivity. Optimising the model for a different type of supercomputer is a matter of applying different transformations using the PSyclone tool rather than rewriting the code, simplifying what can be a costly and error-prone process.”

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