Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cloud formation and distribution follows simple thermodynamic, statistical laws

24.07.2018

The result: An easier way to model cloud cover

Take a look at the clouds, if there are any in your sky right now. If not, here are a few examples. Watch the billows, the white lofty tufts set against the blue sky. Or, depending on your weather, watch the soft grey edges smear together into blended tones that drag down through the air to the ground.


The full 205 km x 205 km domain simulation domain. One hour of time is simulated, with five minutes per frame. Yellows and reds are updrafts, blues are downdrafts, and the grey surface denotes air of a certain temperature.

Credit: Ian Glenn

They're an inspiration to most of us, but a nightmare for climate scientists. Clouds are exceptionally complex creatures, and that complexity makes it difficult to predict how and where they'll form - which is unfortunate, since those predictions are essential to understanding precipitation patterns and how our climate will change in the future.

But University of Utah researchers may have found a way to greatly reduce the difficulty of predicting formation of clouds. The results, published today in Journal of Geophysical Research-Atmospheres could fill a key gap in scientists' understanding of how climate change may play out.

... more about:
»Atmosphere »Humidity »clouds »droplets »heat »thermodynamic

"We used simple thermodynamics," says atmospheric sciences professor Tim Garrett, "to predict that there should be many small clouds and few large clouds in proportions that obey simple mathematical laws."

Clouds are climate wild cards

Clouds, particularly those in the tropics, are part of the Earth's system for getting rid of excess heat generated by the sun. That's why they matter to climate scientists. They're part of a vertical conveyor belt, lifting hot buoyant air up to an altitude where the heat can be easily radiated into the cold blackness of space. But clouds can play with heat in other ways.

"Think of how quickly a cloud can change the temperature during a summer picnic," says postdoctoral scholar and study co-author Ian Glenn. "A slight change in the fraction or distribution of even a few small clouds on an otherwise nice clear day can make or break an outing."

Clouds constantly grow and shrink as they exchange air with surrounding dry air. So far, it's unclear how clouds factor into the effects of global climate change - will clouds slow down warming? Or enhance it? Will warming create more clouds? If so, what regions will be most affected?

That uncertainty can be seen in the range of values of climate sensitivity, or the temperature response to a doubling of carbon dioxide in the atmosphere. Current projections say the increase could be between 1.5 and 4.5 degrees Celsius. It's difficult to pin it down much more than that because of the problem of understanding the role of clouds and precipitation in a changing climate.

"Both the low range and high range are bad news for civilization," Garrett says, "but one is clearly far more catastrophic - so it's a pretty important problem to get right."

Clouds are deeply complex

Researchers previously approached the problem of clouds by trying to understand the layers of complexity inherent in how clouds interact with the surface, the air and even themselves. Study co-author Steven Krueger says that the physical processes in clouds range from cloud droplets, at the micrometer scale, to large-scale cloud systems that can stretch over a continent. And the inherent turbulence of clouds creates eddies - spirals of turbulent energy - that stretch the predictive power of even the best models of clouds run on supercomputers.

"To model all scales of the global atmosphere, from the smallest turbulent eddies to the global scale would take about a billion billion times what can we currently use in our computers," Krueger says. "We can fully calculate all of the cloud physics in a volume about 1 meter on a side, for about 10 minutes, at a computational cost of 10,000 CPU hours."

To get around that complexity, climate modelers simulate large scales while making simplifying assumptions about small-scale processes. But what if there's another way - what if clouds follow simple mathematical principles that can recreate the statistics of clouds' complexity without needing massive computing resources?

Clouds are leaky conduits

Let's go back to the concept of clouds as conduits of heat into the upper atmosphere. A tall, sharp, white cloud is composed of droplets of water, in contrast to the clear, blue, relatively drier air around it. The white, wet clouds and the blue, dry air are in constant contact with each other, sharing a common boundary. It's this boundary that got Garrett thinking.

As water droplets form inside clouds, a little bit of heat is released, making the clouds buoyant in the atmosphere. Garrett says that this makes clouds efficient at their job of lifting heat away from the ground - and also means that the hot, rising air is turbulent and can spill out of the sides of the cloud as it rises.

"This realization about clouds as leaky conduits made me think that the place to look for understanding clouds and climate was not their areas looking down, as has commonly been the focus, but instead their edges," Garrett says.

He began studying the thermodynamics along the perimeters and edges of clouds, and found that the total horizontal perimeter of clouds, turbulent exchanges of heat and humidity across cloud edges and the vertical temperature and humidity profile of the atmosphere could all be related. One notable upside: atmospheric vertical temperature and humidity profiles are relatively simple to predict in changing climates so the link to cloud amount simplifies a notoriously difficult problem.

Some other principles of cloud dynamics that arose from the authors' equations: Competition among clouds for atmospheric heat and moisture helps explain how many clouds form. The product of the number of clouds and their perimeter remains constant, a mathematical law known as scale invariance. This means that a large number of clouds are poor in perimeter while a lucky few are rich. Also, these relationships between different size classes of clouds turn out to be independent of the atmospheric temperature. More on that in a minute.

Garrett and his colleagues tested their theoretical findings by comparing their statistical model to one of the mega-models of cloud formation, the Giga-LES model. It simulates a full 24 hours of atmospheric time over a 150-square-mile (400-square-kilometer) area at high resolution. One 24-hour simulation takes 300,000 processor hours to complete. Garrett's model, based on just a few lines of physics equations, reproduced key statistics of the sizes and shapes of clouds in the dynamic Giga-LES model to within 13 percent.

There are things a statistical model can't do, of course. "It cannot show, for example, a cloud looking like Mickey Mouse showing up at a particular time or place," Garrett says, "so it is best suited for predictions about long-term climate rather than short-term weather."

Clouds follow the rules

So, what does this mean for climate change modelers who want to know how clouds will react to warming global temperatures?

"This is quite speculative," Garrett says, "but the suggestion of our study is that cloud-climate feedbacks may be small, because tropical clouds will rearrange themselves in a warmer climate so as to continue their currently low impact on surface temperatures." In other words, while the total amount of cloud cover may go up, the proportions of cloud sizes at different altitudes likely won't change much. If this model is proven out, climate scientists may be able to breathe a little easier knowing that clouds likely won't be amplifying global warming.

"If these cloud feedbacks are smaller than previously expected," Garrett says, "the Earth may not warm as fast as our worst fears."

Read the full study here.

Media Contact

Paul Gabrielsen
paul.gabrielsen@utah.edu
801-505-8253

 @uofunews

http://www.unews.utah.edu/ 

Paul Gabrielsen | EurekAlert!
Further information:
https://unews.utah.edu/clouds/
http://dx.doi.org/10.1029/2018jd028803

Further reports about: Atmosphere Humidity clouds droplets heat thermodynamic

More articles from Earth Sciences:

nachricht Underwater telecom cables make superb seismic network
02.12.2019 | University of California - Berkeley

nachricht Solving fossil mystery could aid quest for ancient life on Mars
28.11.2019 | University of Edinburgh

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The coldest reaction

With ultracold chemistry, researchers get a first look at exactly what happens during a chemical reaction

The coldest chemical reaction in the known universe took place in what appears to be a chaotic mess of lasers. The appearance deceives: Deep within that...

Im Focus: How do scars form? Fascia function as a repository of mobile scar tissue

Abnormal scarring is a serious threat resulting in non-healing chronic wounds or fibrosis. Scars form when fibroblasts, a type of cell of connective tissue, reach wounded skin and deposit plugs of extracellular matrix. Until today, the question about the exact anatomical origin of these fibroblasts has not been answered. In order to find potential ways of influencing the scarring process, the team of Dr. Yuval Rinkevich, Group Leader for Regenerative Biology at the Institute of Lung Biology and Disease at Helmholtz Zentrum München, aimed to finally find an answer. As it was already known that all scars derive from a fibroblast lineage expressing the Engrailed-1 gene - a lineage not only present in skin, but also in fascia - the researchers intentionally tried to understand whether or not fascia might be the origin of fibroblasts.

Fibroblasts kit - ready to heal wounds

Im Focus: McMaster researcher warns plastic pollution in Great Lakes growing concern to ecosystem

Research from a leading international expert on the health of the Great Lakes suggests that the growing intensity and scale of pollution from plastics poses serious risks to human health and will continue to have profound consequences on the ecosystem.

In an article published this month in the Journal of Waste Resources and Recycling, Gail Krantzberg, a professor in the Booth School of Engineering Practice...

Im Focus: Machine learning microscope adapts lighting to improve diagnosis

Prototype microscope teaches itself the best illumination settings for diagnosing malaria

Engineers at Duke University have developed a microscope that adapts its lighting angles, colors and patterns while teaching itself the optimal...

Im Focus: Small particles, big effects: How graphene nanoparticles improve the resolution of microscopes

Conventional light microscopes cannot distinguish structures when they are separated by a distance smaller than, roughly, the wavelength of light. Superresolution microscopy, developed since the 1980s, lifts this limitation, using fluorescent moieties. Scientists at the Max Planck Institute for Polymer Research have now discovered that graphene nano-molecules can be used to improve this microscopy technique. These graphene nano-molecules offer a number of substantial advantages over the materials previously used, making superresolution microscopy even more versatile.

Microscopy is an important investigation method, in physics, biology, medicine, and many other sciences. However, it has one disadvantage: its resolution is...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

The Future of Work

03.12.2019 | Event News

First International Conference on Agrophotovoltaics in August 2020

15.11.2019 | Event News

Laser Symposium on Electromobility in Aachen: trends for the mobility revolution

15.11.2019 | Event News

 
Latest News

The impact of molecular rotation on a peculiar isotope effect on water hydrogen bonds

03.12.2019 | Life Sciences

SLAC scientists invent a way to see attosecond electron motions with an X-ray laser

03.12.2019 | Materials Sciences

Focused ultrasound may open door to Alzheimer's treatment

03.12.2019 | Medical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>