As climate change looms, researchers are scrambling to answer the question of how a warming planet will affect the frequency and severity of already-deadly hurricanes. Now, a team of researchers from the University of Illinois’ Department of Atmospheric Sciences are using supercomputing in an attempt to answer that question.

Studying weather in a changing climate requires immense computing power and two nested models: first, a climate model to study the effects of greenhouse gases and other stressors on the climate; second, a finer-resolution model to study the effects of those changes on weather phenomena. 

To run these models, Ryan Sriver (associate professor of atmospheric sciences at the University of Illinois at Urbana-Champaign) and his research team utilized the nearby Blue Waters supercomputer at the National Center for Supercomputing Applications (NCSA). Their goal: to run the ultra-high resolution simulations on sufficiently long time scales to understand the interplay between tropical cyclones and climate change.

“Using Blue Waters, we’ve been able to run a suite of computationally-expensive experiments where the atmosphere model is simulating storms spontaneously, thus creating its own climate with tropical cyclones,” said Sriver. “Then, we couple the atmosphere model to the ocean because tropical cyclones get their energy from the warm, near-surface waters. We wanted to see what is the effect of climate-induced changes in the ocean on the storms themselves when we go to a fully coupled, high-resolution climate model configuration.”

“Our research impacts atmospheric science as a whole by really pushing the limits of how we simulate climate change,” said Sriver. He highlighted the importance of Blue Waters’ supercomputing power – roughly 13 petaflops, delivered by a hybrid Cray machine with over 1.5 petabytes of memory and around 26 petabytes of storage. “The computational power Blue Waters allows,” he said, “really lets us diagnose weather-scale processes within a global climate model.” Sriver said that his team was able to get more hours on Blue Waters than were available on other HPC systems by “orders of magnitude.”

The researchers highlighted another major theme of the research: “What is the fundamental role of tropical cyclones in a climate system?” asked Hui Li, a postdoctoral associate from Yale University. “Meaning: how do these weather events affect the main climate state? And this, I think, is the most exciting part, because it shows that this model’s self-generated events can affect the climate’s mean state, which has important implications for our projections of future climate.”

“What we find,” elaborated Sriver, “is that when you allow the ocean to become interactive (i.e. coupling the two models), it changes tropical cyclones considerably, both directly, because of the amount of energy that’s available to the storms from the ocean, but also indirectly, because the model climate state changes, which then has indirect effects on how tropical cyclones behave within the system.”

On initial runs, the research found that interactive mixing with the ocean – which cools the storm – reduced cyclone intensity. But when they ramped up carbon dioxide concentrations in the simulation, the ocean warmed, causing two main effects: first, vertical wind shears, which inhibited cyclone formation; and second, more intense storms from the warmer oceans. In short: fewer, stronger storms.

The team also produced a number of detailed visualizations, which can be seen in the video below. “We’ve been working a lot with the [Blue Waters] data analytics and visualization group producing very high quality animations,” Sriver said. “This is a real challenge because we’re dealing with massive amounts of data.”

“The impacts on society, I think, are substantial,” said Sriver. “This work really paves the way for new modeling endeavors in coupled climate modeling. Because of Blue Waters, we have been able to push the limits of earth system modeling in terms of analyzing short-term extreme weather within a longer-term framework of climate change and anthropogenic global warming.”