UNH Engineer Wins NSF CAREER Award
Study of Langmuir circulation could aid weather forecasting

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DURHAM – If you spend time on the water, you may have noticed a curious phenomenon that is the subject of a University New Hampshire (UNH) professor’s $472,000 National Science Foundation (NSF) grant.

When the wind is blowing just right, foam and flotsam line up in long streaks, roughly pointing in the same direction as the wind. Sailors call them windrows, for they are reminiscent of fields of hay raked into rows to dry. But to Greg Chini, an assistant professor of mechanical engineering in the UNH College of Engineering and Physical Sciences (CEPS), they are evidence of something happening beneath the surface that scientists call Langmuir circulation.

An expert in fluid dynamics, Chini recently received a five-year NSF CAREER Award to study what role this little-understood phenomenon might play in the larger ocean. His research may ultimately
help to improve weather forecasts and climate
predictions.

First described by Irving Langmuir in 1938, Langmuir circulation is driven by the wind and consists of horizontal spirals of current. Adjacent spirals, or Langmuir cells, rotate in opposite directions and so create windrows by pushing anything floating on the surface into the spaces between them.

Langmuir circulation is important because it acts like a giant mixing machine in the top layer of the ocean – the interface between the atmosphere and the deep ocean. This “mixed layer” controls the exchange of heat and gases, such as CO2, the chief suspect in global warming. It extends to a depth of about 325 feet and, compared to deeper layers, is relatively uniform in temperature, salinity and density.

Chini will work with graduate and undergraduate students to determine how Langmuir circulation interacts with “internal waves” that travel just beneath the mixed layer, where temperatures drop sharply. Anyone who has felt the chilly water near the bottom while swimming in a lake is familiar with this layer, called the thermocline.

Chini won’t be spending any time in or on the water, however. His research is theoretical requiring only paper, pencil and a computer. “The amazing thing about nature is that it can be described in mathematical terms,” he said. “I use mathematics to try to understand flow physics. The challenge is to filter out inessential details so that the essence of what’s going on can be identified and understood.” Chini will check his theoretical results against observations of actual Langmuir circulation gathered by Professor David Farmer, dean of the Graduate School of Oceanography at the University of Rhode Island.

By determining if Langmuir circulation increases or decreases internal wave activity in the thermocline, or if internal waves promote or limit Langmuir circulation, Chini hopes to provide weather and climate modelers with a better understanding of the effects of the mixed layer. Current climate models operate on a scale too large to include the mixed layer, so scientists must plug their best guess of its effects into their equations; model predictions can vary significantly depending on what they guess.

While his research won’t get him off dry land, Chini, a native of New York, can trace his interest in fluid dynamics to time spent on the water. “I grew up fishing for muskies with my father on the Saint Lawrence River, spending long hours watching waves and wakes from the boats,” he said. “Somehow that fascinated me and I wanted to describe what I saw quantitatively.”

Chini is the second CEPS researcher in recent months to receive a CAREER Award – one of NSF’s most prestigious awards for new faculty members. Jo Daniel, assistant professor of civil engineering, was awarded a $400,000 NSF CAREER grant in December to study “viscoelastic” materials, such as asphalt. The CAREER award recognizes and supports the early career-development activities of those teacher-scholars who are most likely to become the academic leaders of the 21st century. Awardees are selected on the basis of creative, career-development plans that effectively integrate research and education.

Five other CEPS faculty currently working on NSF CAREER grants, including Carmela Amato-Wierda, associate professor of material science; Karsten Pohl, assistant professor of physics; Elizabeth Varki, associate professor of computer science; Liming Ge, professor of math; and Robert Griffin, assistant professor of earth sciences.

PHOTO CAPTION
Curious Phenomenon: Greg Chini, UNH assistant professor of mechanical engineering, at the computer where he will do much of his theoretical investigation of Langmuir circulation. On the screen is a photo of "windrows" created by actual Langmuir circulation.

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