(Photo by Norbert
Untersteiner, 1957)
(September 18, 2015) Yale
University scientists have answered a 40-year-old question about Arctic ice
thickness by treating the ice floes of the frozen seas like colliding molecules
in a fluid or gas.
Although today’s highly precise satellites do a fine job of
measuring the area of sea ice, measuring the volume has always been a tricky
business. The volume is reflected through the distribution of sea ice thickness
— which is subject to a number of complex processes, such as growth, melting,
ridging, rafting, and the formation of open water.
For decades, scientists have been guided by a 1975 theory
(by Thorndike et al.) that could not be completely tested, due to the unwieldy
nature of sea ice thickness distribution. The theory relied upon a term that
could not be related to the others, which represented the mechanical
redistribution of ice thickness. As a result, the complete theory could not be
mathematically tested.
Enter Yale professor John Wettlaufer, inspired by the staff
and students at the Geophysical Fluid Dynamics Summer Study Program at the
Woods Hole Oceanographic Institution, in Massachusetts. Over the course of the
summer, Wettlaufer and Yale graduate student Srikanth Toppaladoddi developed
and articulated a new way of thinking about the space-time evolution of sea ice
thickness.
The resulting paper appears in the Sept. 17 edition of the
journal Physical Review Letters.
“The Arctic is a bellwether of the global climate, which is
our focus. What we have done in our paper is to translate concepts used in the
microscopic world into terms appropriate to this problem essential to climate,”
said Wettlaufer, who is the A.M. Bateman Professor of Geophysics, Mathematics
and Physics at Yale.
Wettlaufer and co-author Toppaladoddi recast the old theory
into an equation similar to a Fokker-Planck equation, a partial differential
equation used in statistical mechanics to predict the probability of finding
microscopic particles in a given position under the influence of random forces.
By doing this, the equation could capture the dynamic and thermodynamic forces
at work within polar sea ice.