Fancy Tinkering With The Atmosphere? The Derecho Supercomputer Can Advise

In hopes of mitigating the effects of climate change, scientists working in collaboration with the United States National Center for Atmospheric Research (NCAR) are using supercomputers to explore the risks and benefits of seeding the atmosphere with aerosols that would block sunlight and lower global temperatures.

The idea is to mimic natural processes that have been shown to have a cooling effect on the climate. For instance, we've long known that volcanic eruptions can loft compounds high into the stratosphere, and reflect solar radiation back into space.

Proposals to inject aerosols into the stratosphere artificially are nothing new. However, there are longstanding concerns surrounding geoengineering and worries that the impact on the broader climate posed by stratospheric aerosol injection (SAI) isn't well understood – as highlighted in a 2021 paper published by the top boffins at the US government National Academies of Sciences, Engineering, and Medicine.

And of course there's Superman III. We all know how that worked out.

Not the biggest, but aiming to be the best

However, that could soon change. The use of SAI is one of 15 research projects that the recently completed Derecho supercomputer – located in Cheyenne, Wyoming – will tackle. The system, which came online earlier this month, will service the NCAR Accelerated Scientific Discovery program, and is designed to run large scale computational research into weather and climate models.

The system itself is relatively small – at 19.87 petaflops of peak performance – compared to the big iron deployed by the Department of Energy's National Laboratories. For reference, Oak Ridge National Laboratory's Frontier system is more than 50 times more powerful, at 1.1 exaflops. However, for researchers working in collaboration with the NCAR, it's a pretty substantial upgrade – roughly 3.5x that of the outgoing Cheyenne system, built back in 2018.

According to Irfan Elahi, director of NCAR's high performance computing division, the system is designed to meet certain benchmarks for climate and weather research – not to compete in the Top500 for the highest LINPACK score.

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The system itself won't surprise anyone who's been following US supercomputer development in the past few years. It's built by HPE using the Cray EX platform, and is powered by AMD's Epyc Milan CPUs and Nvidia's A100 GPUs. Specifically, Derecho packs 2,488 compute nodes, each with a pair of 64-core Epycs, and 82 GPU nodes with four A100 accelerators each.

While that's relatively few GPUs – just 328 compared to the system's 4976 CPU sockets – Elahi notes that they actually account for about 20 percent of the system's sustained compute capacity. What's more, as researchers work to accelerate their workloads, the Cray EX platform provides room for additional GPU nodes – though Elahi notes that whether or not that happens is going to depend on additional funding.

As it stands, many weather and climate models – including NCAR's Community Earth System and Weather Research and Forecasting models – can't take advantage of GPU acceleration just yet.

"We're very aware that not all of our current code is GPU ready, but the idea is that this will provide the launching pad and platform for our scientists and our users to migrate and accelerate their science with GPUs," Elahi explained. "We're not just looking at what can be done today, but what is possible tomorrow."

Climate scientists' delight

Among the first to get their hands on the system are researchers at Colorado State University, who plan to use Derecho to model large ensemble simulations to assess the influence of climate change on convective storms in South America.

The researchers hope these models will help shine a light on the impact of stratospheric aerosol injection on weather patterns closer to the surface. One major concern around SAI is that using it to lower global temperatures could cause weather patterns to shift in a way that has unexpected consequences – like reduced crop yields due to drought.

This is just one of several research projects planned for Derecho. Researchers at the University of California Los Angeles will use the system to study climate conditions in the western United States that contribute to extreme heat and fire risks. Meanwhile, researchers at Johns Hopkins University will simulate the effects of solar winds – energized particles from the Sun – on the Earth's magnetosphere.

All told, there are 15 university and NCAR projects – on topics ranging from wildfires and hurricanes to solar storms – which will start running on Derecho this summer. ®