Polar sea ice and climate change
and the rest of the sea ice group:
J. Lin, D. Lubbers, C. Furse, and K. M. Golden, Fluid permeability and structure of Antarctic sea ice (invited paper), Deep Sea Research II Special Issue: Southern Ocean Dynamics and Biogeochemistry. Submitted.
K. M. Golden, H. Eicken, A. Gully, M. Ingham, K. A. Jones, J. Lin, J. Reid, C. Sampson, and A. J. Worby, Electrical signature of brine percolation in sea ice. Preprint in final preparation for submission to Geophysical Research Letters.
E. Cherkaev, K. M. Golden, J. Lin, and C. Orum, Algorithms for recovery of microstructural parameters in composite materials. In preparation for Journal of Computational Physics.
A. Gully, J. Lin, E. Cherkaev, and K. M. Golden, Polycrystalline bounds on the complex permittivity of sea ice. In preparation for Journal of Geophysical Research.
Fluid Permeability of Sea Ice
As a boundary layer between the ocean and atmosphere, sea ice plays an important role in the global ecosystem. Sea ice is composed of a porous ice matrix with vertically oriented brine inclusions or channels. Depending on the temperature, salinity, and microstructure, sea ice can allow for the transport of fluid such as sea water or surface meltwater. This fluid transport plays a role in snow-ice formation, heat exchange, nutrient transport, and melt pond evolution by mechanisms that are not well understood.
Along with three other researchers from the University of Utah (Ken Golden, Cynthia Furse, and David Lubbers), I traveled to Antarctica as part of a research expedition in 2010. Stationed in a field camp near Ross Island, we extracted ice cores in McMurdo Sound and measured the electrical properties of the ice as a function of depth. The resulting boreholes were used for permeability measurements, in which the rate at which the water rose was recorded. The crystallographic structure of the ice was also sampled and recorded as a function of ice depth. The vertical permeability and resistivities were computed as a function of brine volume fraction. Our measurements were further corroborated by numerical simulations and comparisons with existing theoretical models. This correlation between electrical resistance and fluid permeability is the basis for further extension into remote sensing techniques for monitoring fluid transport through sea ice, which will be used to improve existing predictive climate models.
Polycrystalline structure of sea ice:
Using tomographic data from ice samples, we numerically generated ice crystals and computed the effective permittivity of these crystals. The data from hundreds of ice crystals was compared against bounds on the effective permittivity of a polycrystalline structure built from these individual crystals. These theoretical polycrystalline bounds and the numerical comparative data, in a joint work with Adam Gully, Elena Cherkaev, and Ken Golden, are presented in a paper, currently in preparation, for the Journal of Geophysical Research.
Recovery of microstructural parameters:
To explore algorithms that recover the microstructural parameters of composite materials, we created random configurations of disks in a bounded domain. Given the area fraction of the disks and a specific parameter of minimum separation between disks, we numerically computed the effective permittivity of hundreds of configuration over a range of frequencies. This frequency-dependent data was inverted using two different, theoretical and numerical algorithms to recover the area fraction and separation between disks. These results, in a joint work with Chris Orum, Elena Cherkaev, and Ken Golden, are presented in a paper, currently in preparation, for the Journal of Computational Physics.
Electrorheological (ER) Fluids:
We have studied the behavior of ER fluids under the influence of an electric field. Using a finite element commercial package COMSOL, we have studied the energy landscape of different, static configurations for a small number of spheres in a small grid and a large number of spheres in a small grid. Ranking configurations in order of increasing energy, we explored the process of how spheres in ER fluids create chains and the possible presence of an energy barrier. Using previously studied equations of motion that take into account the fluid medium and the effect of surrounding spheres, we numerically modeled the movement of dielectric spheres in an insulating fluid. Taking this a step further, we vary the repulsion and attraction forces. We found that vertical connections were easily simulated, and different degrees of branching were attained depending on the repulsion and attraction forces used. These time varying simulations were also used to study the energy landscape during the process of chaining. Our collaborators, Shunbo Li and Ping Sheng, at the Hong Kong University of Science and Technology have provided experiments of ER fluids in the dilute concentrations to study simple interactions. We’ve used these experiments to compare with computer simulations and found similar behavior.