Cloud Computing and Blue Sky Thinking: An atmospheric scientist illuminates the science of clouds in Earth’s sky and beyond

Studying the physics and microphysics of cloud formation and behavior in the laboratory helps scientists understand our planet and those light years away

WEST LAFAYETTE, Ind. – Alexandria Johnson does hard science on the nebulest of topics: clouds. As an atmospheric scientist and assistant professor of practice in Purdue University’s College of Science, she studies clouds wherever they happen to be: in her lab, on Earth, throughout the solar system and in the galaxy.

“The coolest thing about my research is that I can see clouds every day,” Johnson said. “I can look up into our atmosphere and see them change and evolve. Then I can take that knowledge and apply it to other planetary bodies, both within and beyond our solar system.

Cloud science covers a lot of ground. His research sheds light on topics ranging from rainfall and microplastics in Indiana to the climates of moons and planets far outside the realm of human experience.

Clouds in a bottle and a storm in a teacup

The study of clouds in their natural environments can be complex and subject to variations in climate, weather and observation devices. Johnson’s solution is to create his own homegrown clouds to study in his laboratory in the Department of Earth, Atmospheric and Planetary Sciences. He strips systems down to their basics to gain a clear understanding of how the particles that make up clouds form, develop, and interact with their environment. Nothing in his lab really looks like a cloud; there are no mists swirling picturesquely in glass bottles. They are mainly lasers and large black boxes. But the behavior of these lab-based cloud particles mimics the behavior of cloud particles in huge clouds sweeping across the sky, just in miniature.

“Of course, we don’t grow them at the same scale that you see in an atmosphere,” Johnson said. “Instead, we can take a representative particle of a cloud, pump in different gases and change the temperature and pressure of the system. We then watch as that particle grows, shrinks or changes phase over time, which are processes that happen everywhere in clouds.”

Clouds on Earth don’t often form without the help of a nucleus, or a particle, and in some cases what would be considered a nucleus on Earth might be an exotic cloud elsewhere. The particles in Johnson’s lab, like all particles, have a charge. Johnson and his team use an electric field to levitate and contain individual particles so they can’t move. These particles are then stable over long periods of time, which allows for long-term research experiments, where pressure, temperature, electric field and laser illumination can be changed and observations recorded. Other methods build on these to allow the team to look at groups of particles and see how they scatter and polarize light.

Using methods like these, Johnson can study how clouds form and what the different shapes and compositions of cloud particles can reveal, and he is able to understand the conditions that lead to different cloud types and behaviors. Like aeronautical engineers who use a wind tunnel to observe how currents move around structures, Johnson uses these particles to understand the microphysics that underlie large and complex systems.

Many scientists—climatologists, meteorologists, and planetary scientists, to name a few—study clouds as part of their larger research. But Johnson is one of the few who studies the particular physics of clouds in the laboratory.

“Not many of us delve into the microphysics of how clouds form,” Johnson said. “Anyone who studies the atmosphere has a general sense of knowledge about clouds. But none of these systems work without physics. We need to understand microphysics to truly grasp its intricacies and implications.”

There is always a silver lining

It’s a long-running joke that the nights of major astronomical events on Earth seem to be almost preternaturally apt to be cloudy. This also applies to other planets.

Using huge, advanced and very powerful telescopes, astronomers can peer across miles and light years of space only to find clouds blocking their view of the planet itself. Rather than the planet’s surface, they can only sense the opaque atmosphere that envelops it.

Every planetary body in the solar system that has a thick atmosphere, and many outside it, have clouds in that atmosphere. Even bodies with thin, thin, or intermittent atmospheres, such as Pluto, have particles suspended in the atmosphere which, while not true clouds, are a haze of particles and share many of the properties of clouds.

“Clouds are a ubiquitous feature of planetary atmospheres,” Johnson said. “This is something we’ve seen from our own solar system, and when we look at the atmospheres of exoplanets, it’s no surprise that we find clouds there as well. Unfortunately, they tend to block our view of the atmosphere below.

Scientists have been able to send probes and rovers to nearby planetary neighbors, including Venus and Mars. But for bodies that are farther away, including exoplanets — planets entirely in other star systems — scientists need to find clever ways to conduct the science.

“Astronomers find clouds to be a nuisance. They get in the way of the data they want, whether it’s knowing the surface of the planet or its atmospheric composition,” Johnson said. “We see it a little differently. Yes, there are. We can’t get rid of them. our understanding of clouds on Earth and the planetary atmospheres of our solar system to learn about these things we can’t observe in exoplanets.”

Most of the planets Johnson studied are “cool” planets. While Earth looks balmy (with an average planetary temperature of about 60 degrees Fahrenheit), it’s actually cool by planetary standards, when compared to the large gas giants that orbit close to their stars like the hot Jupiters.

Johnson and his team accumulate information about planetary bodies in Earth’s solar system or about exoplanets. Astronomers can collect spectrographic data to analyze the chemical compounds that make up the atmosphere and use mathematical models, observations and gravitational studies to determine a planet’s mass, velocity and orbit. By combining this information with insights from his laboratory studies, Johnson can help astronomers determine what a planet’s atmosphere might be like and extrapolate its potential to harbor life.

“Our big questions are when, where and why do clouds form in these atmospheres?” Johnson said. “If we want to understand these enveloped exoplanets, we need to understand clouds. This understanding gives us insight into atmospheric chemistry at work, atmospheric circulation, and climate. In a certain sense we base the truth on astronomical observations”.

Now both sides

Johnson is also watching the clouds from below, a little closer to home. In a current study, he is examining the role microplastics play in cloud formation. Microplastic pollution, which has been found just about everywhere, including large bodies of water like the Great Lakes, can form part of clouds or be swept away by precipitation, then flood the landscape with thunderstorms and snowfall. Those microplastics have dire implications for ecosystem health, human health, and agriculture.

Understanding how they attach to clouds, move through weather systems and affect the landscape as they settle can help Johnson and his team protect life on Earth, just as they explore the possibility of livable conditions on other planets.

“It’s the same physics,” Johnson said. “It’s the same processes, all over the universe, and it brings me a tremendous amount of wonder and joy. As an undergraduate physics student, I took on a senior research project investigating how water droplets freeze under varying conditions. I have literally watched a droplet freeze hundreds of times to study the process and have been mesmerized. I said, ‘This is what I want to do with my life. This is great. I want to study the clouds.’”

About Purdue University

Purdue University is a leading public research institution developing practical solutions to today’s toughest challenges. Ranked in each of the past five years as one of the 10 most innovative universities in the United States by US News & World Report, Purdue offers world-changing research and out-of-this-world breakthroughs. Committed to real-world online and hands-on learning, Purdue offers a transformative education for all. Committed to affordability and affordability, Purdue has frozen tuition and most fees at the 2012-13 levels, allowing more students than ever to graduate debt-free. See how Purdue never stops in the persistent search for the next giant leap https://stories.purdue.edu.

Writer/Media Contact: Brittany Steff, bsteff@purdue.edu

Source: Alexandria Johnson, avjohns@purdue.edu