Arctic sea ice may look like a continuous frozen surface from a distance. Up close, much of it is a shifting collection of individual slabs called floes, pushed by winds and ocean currents and repeatedly colliding with one another.
Those collisions could help explain how sea ice moves across the Arctic on much larger scales, according to research by UC Riverside engineers published in Physical Review Letters and selected as an Editor’s Suggestion for the cover of the journal.
The study, “Anomalous Statistics of Sea Ice Transport are Explained by Collisional Rules”, was led by Bryan Shaddy, who began the work as an undergraduate studying mechanical engineering at UCR. Shaddy later pursued his doctorate at the University of Southern California and is now a postdoctoral scholar at CTrees.
His co-authors are Alex Greaney and Bhargav Rallabandi, associate professors of mechanical engineering in UCR’s Marlan and Rosemary Bourns College of Engineering.
Predicting the movement of sea ice is difficult in part because of the enormous difference in scale. Researchers can measure properties of individual ice floes and their local environment, but climate models need to represent how vast fields of ice move and spread.
Rallabandi and his collaborators found that the connection between those scales can emerge from a relatively simple physical process.
They developed a computer simulation that treats sea ice as a collection of particles driven by fluctuating winds. In densely packed ice, floes collide with their neighbors much more frequently than the wind changes. Each collision dissipates some of the energy supplied by the wind and transfers motion among neighboring floes.
Using measurements of local wind conditions and properties of the ice as inputs, the model reproduced several characteristics of sea ice observed in the Fram Strait, a major passage between Greenland and the Svalbard archipelago. These included how the ice disperses over time and the distribution of floe velocities.
The findings connect properties that can be measured locally, such as the characteristics of individual floes and their environment, with patterns of sea ice transport occurring over much larger distances and longer periods.
Those larger-scale patterns are difficult to measure directly, but they matter for climate models because they help determine how rapidly sea ice spreads. By connecting them to measurable properties of individual floes and their environment, the researchers have developed a way to better understand sea ice transport across much larger scales.
Rallabandi said the findings could help researchers more accurately represent sea ice in climate models. The underlying physics may also apply to other systems in which objects interact and collide in a changing environment, including avalanches and landslides.