SCD News: August 3, 2005
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From sea breezes and plumes of smoke to drifting snow and billowing fog banks, turbulent flows are found everywhere in the Earth system. These characteristic and repeating patterns of irregular, eddying motions are called “coherent structures” in turbulence research, and took center stage during a four-day workshop held at NCAR July 11-14, 2005.
The workshop, called “Coherent Structures in Atmosphere and Ocean,” was sponsored by the Geophysical Turbulence Program (GTP) of NCAR's Institute for Mathematics Applied to Geosciences (IMAGe). Joe Tribbia of GTP co-organized the workshop with Jean-Marc Chomaz (Ecole Polytechnique/LadHyX, France) and Yoshi Kimura (Nagoya University, Japan).
About 75 participants gathered from numerous research disciplines and international institutions to survey the functions of coherent structures in geophysical turbulence.
Geophysical turbulence, which is responsible for mixing and transporting elements such as moisture, heat, salinity, and energy across the globe, plays a crucial role in many environmental processes. Understanding coherent structures and how they evolve and interact is a priority for researchers who track the movement of oceans and atmosphere.
“Coherent structures are vortices that give the structure of the flow in the atmosphere, in the ocean, all over the planet—which is why we think they're so important,” said Chomaz. “You see them at all scales, from small dust devils to tornadoes and cyclones that are thousands of times bigger. It's important to understand the dynamics between all these scales to understand the dynamics of the atmosphere.”
But the nonlinear, unpredictable behavior of these structures is highly complex, and at the relatively coarse resolution of current global circulation models, direct numerical simulation of most geophysical flows is not yet possible. Scientists must use numerical techniques such as statistics and parameterization to represent them.
“In weather forecasting today, we only grab the large vortices,” said Chomaz. “Even a hundred years from now, computers won't be powerful enough to compute vortices that are human-size and smaller. But we need to know how these structures interact, to have theoretical and practical descriptions of the effect of small vortices on large vortices. The way this occurs is still not fully known—we know part of it, but not all. This is why there are so many discrepancies in models of climate change: the small scales are not included in the models. We must put forth a theory of that interaction.”
Discussing theories was an important focus of the workshop, which brought together atmospheric scientists, computational scientists, mathematicians, physicists, and engineers from the U.S. and abroad. Participants also had a chance to share experiments and observations and compare numerical methods.
“What's exciting is that we've got people from different areas getting together and seriously discussing mutual interests,” said Kimura.
“There were a great many people coming at the problem from various perspectives,” added Tribbia. “It was educational for everyone. I think it was a large success, primarily because of the openness of the discussions that occurred during the meeting and afterwards. There were quite a few excellent presentations, including the poster sessions, and everyone had a kind of natural inquisitiveness.”
Chomaz concurred. “The nice thing about the meeting is that there was a good spectrum of research, from very applied people who were measuring things and getting real data, to those who were doing fundamental research on isolating mechanisms. Some people were looking in the ocean, taking profiles of velocity, salinity, and temperature, observing that there was a sheer, rollers, billows that mix the fluid. Others were doing numerical work to extract the data; they had information on more specific problems. Others were proposing theoretical mechanisms to explain both, the data and numerics. And they were all interacting at the same time.”
Kimura noted that the organizers tried to make the workshop as fundamental as possible. “In many places, science is becoming more and more applied and practical, people are ignoring basic science. We strongly protest such kind of thought. Basic science is useful.”
“This was a typical GTP workshop where people delve deeply into fundamental issues that transcend NCAR divisions, the kinds of problems that are in everybody's mind, as it were,” said Tribbia. “The question of coherent structures in inhomogeneous turbulence—that is, with effects like stratification or magnetic fields—and the general method for attacking those problems are at the core of divisional programs in modeling the atmosphere, ocean, and the sun.”
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Partipants and organizers at the summer 2005 IMAGe workshop discussed theories, shared experiments and observations, and compared numerical methods. Photo gallery |
GTP is a long-standing NCAR program with participants from every division. Its broad goal is to promote research, education, and awareness of geophysical turbulence. Interests of GTP members span the full range of scientific methods: analytical theory, statistical analysis, stochastic modeling, algorithm development, numerical simulation, parameterization, analyses of observational data, field programs, laboratory experiments.
GTP's Turbulence Numerics Team (TNT) is dedicated to the study of turbulence using both theory and numerical simulation with experimental validation. TNT is involved with many turbulence researchers to facilitate fundamental research at NCAR on turbulence and to foster ties with the university research community.
GTP is an activity of IMAGe, an NCAR institute that is missioned with bringing mathematical tools to bear on fundamental problems in the geosciences. IMAGe encourages internal collaborations among NCAR divisions and external collaborations among mathematics centers, universities, and government laboratories. IMAGe activities emphasize grand scientific challenges that are faced in understanding the Earth system, and the subsequent enrichment of the mathematical sciences from tackling such problems.
IMAGe is part of NCAR's Computational and Information Systems Laboratory (CISL).
Photos: Lynda Lester, NCAR/CISL
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