Night Clouds

Laura Zajac
September 01, 2000

A mystical stillness spreads over the coast of Norway as the sun slides slowly into the sea. Shadows lengthen, crevices seem to deepen, and scattered caves appear. Gull cries echo through the fjords. Earlier today, fishing boats dotted the waters, trolling for the day's catch. But now the boats are docked by the villages, scattered handfuls of cottages clinging to narrow stretches of beach.

The evening mist creeps up the rocks; the damp smells of salt and fog fill the air. Folktales tell of trolls in these cliffs: Huge creatures with long crooked noses and a fear of sunlight.

The darkness rises up the cliff-faces, but still the midnight sky glows muted gold. And high, high above the cliffs, just where the dying sunlight meets the blue of dusk, are the clouds. Silvery blue, wispy and mysterious—nocturnal clouds frozen high above the fjords.

yellow clouds in sky

These noctilucent, or "night shining" clouds were first sighted 100 years ago. They have been observed more frequently in recent years, an increase that may be due to a pollution-induced change in our atmosphere. No one knows. "They could be from methane released into the air," said Dirk Padfield, a Penn State student working with electrical engineering professors Charles Croskey and John Mitchell to study these clouds.

The clouds are found near the mesopause, the highest region of the mesosphere, 52 miles above the ground. "Turns out the very coldest temperatures on Earth occur at the mesopause," explained Mitchell. (Summer temperatures of -260 degrees F have been measured.) But the clouds are only visible at night and in the far north. That we can see them at all is due to the curvature of the Earth. As the sun drops behind the horizon, its light, blocked by the Earth, still travels over our heads through the upper atmosphere. The clusters of ice in the mesosphere catch the light and reflect it, causing the event we call noctilucent clouds.

Their location poses a problem for scientists. "Balloons can't go that high, and satellites can't go that low," explained Padfield. The only way to study them directly is to launch a rocket into the middle of one. The study Padfield, Croskey, and Mitchell are working on did just that. Funded by NASA, the project brought scientists from Germany, Austria, Sweden, and the United States to Andøya, or Duck Island, in northern Norway. Each scientist built several probes to be part of the payload of the rocket.

Padfield's main job was to make sure the three Penn State probes worked, and to test them for possible interference with the other probes on the rocket. His other task was simply to learn as much he could about the project.

A double major in electrical engineering and international studies, Padfield had worked for a year in Israel before coming to college, and studied language and religion in Egypt during his sophomore year. He knows three languages. Born in Alaska, he spent the next 12 years of his life on the same coast of Norway that he returned to this summer. It was here that his analytical mind and scientific aptitude first showed themselves. "When I was a kid, I had a notebook, and I would write the times tables in it. I went all the way up to 2000, just for fun; I always really liked math," said Padfield. "Since middle school I've known I wanted to be an electrical engineer; that hasn't changed, and I just enjoy it more and more as I go through." His interest led him to seek out Mitchell at Penn State. "Dirk contacted me through e-mail from Israel," explained Mitchell. He chuckled. "He's the only student I advised before he became a student." So when Padfield approached his adviser last spring asking to do research, Mitchell didn't hesitate to bring him into the rocket project. Padfield's fluent Norwegian was an unforeseen benefit.

"What size are the particles? Are they charged or neutral?" By learning the answers to these questions, Mitchell said, "we can better understand noctilucent clouds." The Penn State probes were designed to detect the electrical charge of the ice particles. Padfield described the first probe, called a Gerdien condenser, as "a bucket with a large whole in the bottom and a little metal cylinder in the middle." The "bucket" was set to zero voltage. The inner metal cylinder had a constantly changing voltage that swept from very negative to slightly positive. As the rocket shot through the cloud, charged ice particles moved through the bucket. Since "opposites attract," positively charged ice particles were attracted to and struck the negatively charged cylinder. As the cylinder became less negative, large particles passed by but small particles were still mobile enough to be attracted. Negative particles struck the cylinder only when the voltage was positive. A sensor in the probe recorded all these hits, and sent the information back to land via radio signals.

By combining the information transmitted back from the Gerdien condenser and the other two probes, the researchers will also be able to estimate the size and density of the ice particles. Padfield explains, "If we can understand the charges and density of the particles, and compare our measurements with those from the other probes on the rocket, then we can have a better understanding of the clouds and where they came from. We can know if the clouds are harmful, if they're caused by pollution, their relation to global warming, and if they're detrimental to the environment."

In May of 1999, the scientists involved in the project gathered at NASA's research base in Wallops Island, Virginia. There the rocket was "basically beaten-up," said Padfield, to simulate possible flight conditions. "They'd shake it to make sure it wouldn't fall apart. They'd compress it, and test it again. Then they checked to make sure all the screws were still in." Afterwards it was taken apart and shipped to Norway.

On Andøya, Padfield and the other researchers reassembled the rocket and retested the probes. Then everyone settled down to await the clouds.

Noctilucent clouds can only be seen from a distance. The launching party could not just look up and aim the rocket at a cloud; lidar and radar were used to pinpoint the cloud's location.

Once the target cloud was identified and the wind was blowing the right way, the rocket was readied for launch. "It really overwhelms you, overwhelms your senses," explained Padfield. "It ignites and the whole thing just blows up underneath. There are big flames and a lot of smoke—it's really loud!" Radar tracked the rocket on its steep path through the sky. After three minutes, the pointed cone of the rocket popped off, exposing the probes. The sensors picked up information for the 10 seconds it took the rocket to pass through the cloud. After peaking at 73 miles above the ground, the rocket rotated and, pulled by gravity, plunged toward Earth, passing back through the cloud and splashing down into the sea. The payload would remain at the bottom of the sea, but the mission was a success.

Padfield is now developing a computer program to interpret the signals sent back from the probes. "I learned what research is," he said of his experience. "It was humbling. In research, the more you learn, the more you understand how much more there is to learn."

Dirk Padfield received a B.S. in electrical engineering and a B.A. in international studies in May 2000, with honors in electrical engineering, from the College of Engineering and the Schreyer Honors College. In May he won an NSF Graduate Research Fellowship. His advisers are John Mitchell, Ph.D., 129 Electrical Engineering East, University Park, PA 16802; 814-863-2788;; and Charles Croskey, Ph.D., 303 Electrical Engineering East; 865-2357; The project was funded by NASA. Padfield's participation was funded by NASA, a Heather L. Rayle Summer Scholarship, and a Schreyer Ambassador Award. Writer Laura Zajac graduated in May 2000 with a B.S. and honors in biobehavioral health.

Last Updated January 10, 2014