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Math Offers Explanations for Meteorological Phenomena

Mathematician Romain Nguyen van yen named Alexander von Humboldt Fellow at Freie Universität

Oct 26, 2011

Satellitenaufnahme des Orkans Kyrill, der im Januar 2007 über Europa fegte und dessen Böen Windgeschwindigkeiten bis zu 225 km/h erreichten.
Satellite image of Hurricane Kyrill, which swept over Europe in January 2007 and whose gusts reached wind speeds of up to 225 km / h. Image Credit: Deutscher Wetterdienst

Turbulence – it’s a word that has come up often in reports on the current situation on the international stock exchanges. But many will also associate it first with the kind of turbulence we hear about in the weather report. After all, these air currents keep things hopping, and not just this past summer, either. This kind of turbulence is the focus of Romain Nguyen van yen. The 27-year-old French citizen has received the Alexander von Humboldt Foundation Research Fellowship, and with help from this prestigious institution, he has been at the Institute of Mathematics at Freie Universität Berlin since March.

His aim: to advance understanding of turbulence from a mathematical standpoint. After all, even if these currents were first identified over a century ago, there is – astonishingly – not yet a solid mathematical theory on the phenomenon as a whole.

In most cases, the first thing Nguyen van yen receives from Professor Rupert Klein for his work within the Department of Mathematics and Computer Science is a gigantic data set, which might include measurements taken in a turbulent current or figures extracted from a numerical simulation of this type of current. One of his tasks is to identify hidden structures that lend an overall sense to these data. To this end, the young researcher has come up with his own method, which was one important factor in his being granted the research fellowship. He divides the numbers into two groups. The first comprises data that reflect large, coherent eddy structures – also termed simply “coherent structures” – within the turbulent air current. The second is made up of data that depict the less structured, or “uncorrelated,” movement of air that also exists in these currents, aside from large eddies.

The idea of splitting up the data in this way is not new in itself, and the literature on the subject includes various suggestions for how to divide the data into coherent structures and uncorrelated air movement. But what is new about Nguyen van yen’s approach is that it draws on advanced mathematical tools in information theory in order to evaluate these suggestions and pinpoint the most efficient ways to solve a particular task.

For example, Nguyen van yen aims to find out, with as much precision as possible, what effect all of the uncorrelated “noise” has on the large eddies, and how the large eddies behave in response. This information could be important to meteorologists and construction engineers alike, for instance in connection with calculating the lift of aircraft wings, where larger and smaller eddy structures form. Thus far, however, researchers have had to rely on semi-empirical approaches to calculate how these eddies affect flight mechanics. A stable mathematical model is still lacking.

It is safe to say that research fellow Nguyen van yen also experienced some turbulence in his winding path to this research field. Born in Paris, Nguyen van yen initially focused on physics, spending four years at the prestigious École normale supérieure (ENS), in Paris, on a scholarship provided by the French government. The young Frenchman, whose last name comes from his Vietnamese grandfather, completed not only a program in physics, but also an exam for math teachers, during his time in the French capital. After that, he decided to embark on a doctoral program.

His dissertation, for which he also received a scholarship, was on a topic drawn from meteorology. “It was back then that I discovered my interest in numerical calculation of turbulence and started my theoretical research.” For Nguyen van yen, who learned German as a second foreign language in school and gained advanced proficiency in German during a two-month intensive course, the project at Freie Universität represents a perfect combination of all of the fields he has studied so far, as he says. And no wonder: After all, he calls himself “a physicist who works a lot with mathematics, studying topics including meteorological phenomena.”

Further Information

Dr. Romain Nguyen van yen, Freie Universität Berlin, Department of Mathematics and Computer Science, Institute of Mathematics, Tel.: +49 (0)30 / 838-75201, Email: