Nav: Home

Technique could help climate models sweat the small stuff

June 03, 2016

PROVIDENCE, R.I. [Brown University] -- A team of physicists and mathematicians has come up with a statistical technique that puts the fine details back into computer simulations of large-scale phenomena like air circulation in the atmosphere and currents in the ocean.

Computer models are generally good at capturing the big picture, but they are often forced to ignore things that happen at small scales. For example, models of a planet's atmosphere capture the large-scale dynamics of jets and airflows, but they don't include small-scale dynamics created by things like clouds and localized turbulence, despite the fact that those dynamics can often influence the larger scales.

"There are simply too many numbers for the computer to simulate it at a reasonable speed," said Brad Marston, a Brown University physicist. "It might take years to simulate a day of the atmosphere, which wouldn't be good."

The traditional approach to dealing with the problem is to simply lop the small scales off of the simulation. A few ad hoc ways of putting some of that information back in exist, but they tend not to be mathematically rigorous.

"These schemes have always suffered from the criticism that they lack predictive power," Marston said. "You have to make a lot of decisions that you really shouldn't have to make but you're forced to make."

In a paper published in the journal Physical Review Letters, Marston and his colleagues show a method of averaging out those small-scale dynamics in a way that is computationally tractable, which allows those dynamics to be simulated and their effects to be captured in a rigorous way.

"We're retaining the degrees of freedom at the small scale, but treating them in a different way," Marston said. "We don't have to simulate all the little swirls, so to speak. We treat them by using their averages and the sizes of their fluctuations. It allows us to capture the contributions of these small-scale dynamics that would normally not be included."

In their paper, the researchers used the technique to model air jets forming on a round surface. They showed that the method produces results similar to brute-force numerical simulations of the same jets.

There have been prior attempts to treat small-scale disturbances statistically, Marston said, but those haven't fared very well. Prior attempts have treated disturbances as being homogeneous and assumed they were not traveling in any one particular direction.

"But that almost never happens in nature," Marston said. "Turbulence almost always has some directionality to it. That directionality is what makes these kinds of approximations work. It makes these approximations tenable."

The researchers hope that the method might make for more accurate simulations of a wide variety of natural phenomena, from how the churning interiors of planets create magnetic fields to how air flows across the surfaces of cars or airplanes.

The method could be particularly useful in modeling Earth's changing climate because the technique can more rigorously capture the influence of cloud formation.

"Cloud formation is seen as the largest source of uncertainty in climate models right now," Marston said. "There are famous examples where different climate models that have different ways of dealing with the clouds give you qualitatively different results. In a warming world, one model might produce more clouds and another might produce fewer."

By averaging those cloud dynamics and then simulating them in the models, it might be possible to reduce some of that uncertainty, Marston said.

The team has already started working to incorporate the method in climate simulations, as well as simulations of ocean currents and problems in astrophysics dealing with the behavior of plasmas.

"There are a whole bunch of problems out there where we feel this could be helpful," Marston said.

Brown University

Related Climate Models Articles:

Scientists argue current climate change models understate the problem
A new study on the relationship between people and the planet shows that climate change is only one of many inter-related threats to the Earth's capacity to support human life.
Climate models may underestimate future warming on tropical mountains
By reconstructing past temperature change on Mount Kenya in East Africa, a new study suggests that future temperature changes on tropical mountains might be underestimated.
New research on shallow warm clouds will advance climate models, weather forecasts
David Mechem is leading a new $525,000, three-year grant from the US Department of Energy to better understand the fundamental processes governing the behavior of shallow clouds.
Uncertainties related to climate engineering limit its use in curbing climate change
Climate engineering refers to the systematic, large-scale modification of the environment using various climate intervention techniques.
Impact of sea smell overestimated by present climate models
The formation of sulfur dioxide from the oxidation of dimethyl sulfide and, thus, of cooling clouds over the oceans seems to be overvalued in current climate models.
More Climate Models News and Climate Models Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...