Dreaming of Hurricanes

When Kim Johnson was 8 years old, she would race through her school work so she could watch the Weather Channel. Her favorite show was “Weather in the Classroom,” and Johnson was in love with the subject. Seeing weather in action gave her a thrill.

Now, the OSU senior and Honors College student from Beaverton, Oregon, is working her way toward a bachelor’s in physics, and she still has that same love for weather. Since she first learned about hurricanes, she has dreamed of studying these raging, destructive forces of nature.

For scientists, hurricanes are physics in action. So with support from a Research Experience for Undergraduates grant from the National Science Foundation, Johnson has been learning about atmospheric radiation, heat transfer and other phenomena, in addition to picking up some advanced mathematics. And she has refined her focus from the continental-scale forces that create storms to the boundaries of a single cloud, where dust, moisture and air currents collide.

“I wanted to learn how clouds form,” says Johnson, “and how the particles they form on affect cloud properties.” So under guidance from Associate Professor Cynthia Twohy in the College of Oceanic and Atmospheric Sciences, she has been getting an intimate look at the seeds on which clouds grow.

Her project is part of a federal research program known as the Rain in Cumulus over the Ocean experiment, or RICO. The goal is to understand the forces that create sub-tropical cumulus clouds, one of the globe’s most prevalent cloud types and a factor in the Earth’s energy balance and climate. Twohy is a principal scientist in RICO.

In a lab bathed in green light, Johnson inserts particle samples into a transmission electron microscope. “An instrument (mounted on an airplane) gathers particles from clouds, evaporating most, if not all, the water along the way” and depositing them on delicate membranes known as grids, she says.

The microscope’s X-ray beam reveals sea salt crystals and dust grains. Black balls of carbon are among the smallest. These particles of soot come from forest fires and fossil fuel combustion. Sulfuric acid is a common component, says Johnson, but it is so volatile that it tends to boil away under the beam.

“Kim’s research will determine whether clouds forming on these particles are different from clean marine clouds,” says Twohy. “This will help us learn how pollution affects cloud properties, one of the largest uncertainties in understanding climate change.”

By combining information about chemical composition with data on trajectory, temperature, wind speed and altitude, scientists can determine the source of the particles. Johnson is excited about her work because she is learning first-hand how the origin of an air mass affects cloud formation and why some clouds generate more rain than others.

“We’re finding that some air trajectories reaching the site are influenced by dust from Africa or pollution from North America or Europe,” Twohy adds.

Johnson’s research has changed the way she looks at the sky. “Clouds look so clean and white, and people think of them as just drops of water. But there’s so much more going on in them. The surface area and size of these particles affects how much water can condense and whether or not rain can form,” she says.

When she is done with a four-hour stint in the lab and isn’t working as a teaching assistant in a physics class, Johnson spends time with friends and family. She has plans for a winter wedding and intends to study meteorology next fall at the University of Arizona, where she aims to get back to her childhood dream of studying hurricanes.

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