Dynamic Observations of the Densification of Polar Firn Under Compression Using a Micro‐Computed Tomograph

Li, Yuan; Baker, Ian

doi:10.1029/2021jf006290

Cited by 6 publications

(2 citation statements)

References 71 publications

(143 reference statements)

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“…The microstructural parameters of interest from the micro‐CT data are the density ( ρ ‐kg m −3 ), the mean structure thickness (S.Th‐mm), the area‐equivalent circle diameter (ECDa‐mm), the specific surface area (SSA‐mm −1 ), the porosity ( φ ), and the degree of anisotropy (DA). For the definition of ρ , S.Th, ECDa, SSA, and φ , see elsewhere (Li & Baker, 2021; Li & Baker, 2022a, 2022b and references therein). The DA is a measure of alignment or 3‐D symmetry in the enclosed region or VOI containing the ice matrix and the air phase.…”

Section: Samples and Methodsmentioning

confidence: 99%

Microstructural characterization of depth hoar and ice‐crust layers using a micro‐CT, and hypothesis of ice‐crust formation under a thunderstorm

Li,

Fu,

Keegan

et al. 2023

Hydrological Processes

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The microstructural features typical of depth hoar and ice‐crust layers in both blocks of snow and a firn core that were extracted at Summit, Greenland (72°35′ N, 38°25′ W) in June, 2017 have been characterized using x‐ray microcomputed tomography (micro‐CT). In the depth hoar, the density is much lower, and the porosity, pore sizes, and specific surface area (SSA) are greater than those in adjacent layers. In the ice‐crusts, the density and the particle size are greater, and the porosity, pore size, and SSA are less than those in adjacent layers. Note that the mean structure thickness in the depth hoar was greater than that in adjacent layers, but that increase was simply related to the one‐ or two‐dimension ice crystals, that is, needle‐like or plate‐like structures, being included in the measurements for depth hoar. Using related microstructural parameters derived from the micro‐CT data, we propose a model based on refreezing of pre‐melted water (PMW) droplets electrostatically‐transported by the electric field between thunderclouds and the ice sheet created by a thunderstorm that describes the processes of the ice‐crust formation (ICF). Whether the ice‐crust forms with depth hoar depends on both the kinetic energy from the PMW droplets and the latent heat liberated from the freezing of the PMW. This work is the first to build the relationship between the atmosphere and ice sheets by a thunderstorm. Finally, we provide an experimental geophysics‐based method through the ICF under laboratory conditions to learn more about the interaction between atmospheric electrodynamics and thermodynamics.

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Section: Samples and Methodsmentioning

confidence: 99%

Microstructural characterization of depth hoar and ice‐crust layers using a micro‐CT, and hypothesis of ice‐crust formation under a thunderstorm

Li,

Fu,

Keegan

et al. 2023

Hydrological Processes

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“…Thus, several microstructural parameters from the micro CT were used to characterize the evolution of the snow microstructure, that is, the density, the structure thickness (S.Th), the area-equivalent circle diameter (ECDa), the specific surface area (SSA), the structure model index (SMI) and the total porosity. These parameters have been defined in detail elsewhere (Chen & Baker, 2010a;Wang & Baker, 2013;Adolph & Albert, 2014;Li & Baker, 2021, 2022.…”

Section: Micro Ctmentioning

confidence: 99%

Metamorphism observation and model of snow from summit, Greenland under both positive and negative temperature gradients in a micro computed tomography

Baker

2022

Hydrological Processes

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Three sets of snow specimens with different initial densities ranging from 311 to 486 kg m À3 , which were collected from depths of 7, 40 and 57 cm at Summit, Greenland (72 35 0 N, 38 25 0 W) in June 2017, were subjected to the temperature gradient (TG) of $160 K m À1 in opposing directions. The snow metamorphism was characterized using both X-ray micro computed tomography and optical microscopy. The formation of depth hoar is evident as the snow grains transformed from the initial approximately rounded particles to needles, broad-plates, columns and cup-shapes.The de-densification process of snow is also reflected in various microstructural parameters, viz., the density and the structure thickness (the feature size of ice particle) generally decreased with time, while the area-equivalent circle diameter (the feature size of pore), the total porosity, the specific surface area and the structure model index (a measure of convexity/concavity of ice surface) increased. Based on an icesphere pair of equal size, a vapour transport model, which depends on the initial particle radius, r p , and the ratio of the initial particle-bond radius to the initial particle radius, α, was constructed to simulate the main characteristics of change in the density with time under the TG metamorphism. We found critical values of r p = 0.1 mm and α = 0.1 that determine how fast the geometric coefficient, ψ (a tuning parameter used in this model at the cone angle θ ¼ 45 between the two ice spheres), changes.We propose a conceptual model in which an ice-sphere pair can be regarded as a volume element of morphogenesis of depth hoar. This model can be used to explain the formation of the needle-like, broad-plate and column depth hoar by combining particle-by-particle with inter-layer vapour transport.

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Critical values of the microstructural parameters at the first critical density of the densification of polar firn

2022

Cold Regions Science and Technology

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Dynamic Observations of the Densification of Polar Firn Under Compression Using a Micro‐Computed Tomograph

Cited by 6 publications

References 71 publications

Microstructural characterization of depth hoar and ice‐crust layers using a micro‐CT, and hypothesis of ice‐crust formation under a thunderstorm

Microstructural characterization of depth hoar and ice‐crust layers using a micro‐CT, and hypothesis of ice‐crust formation under a thunderstorm

Metamorphism observation and model of snow from summit, Greenland under both positive and negative temperature gradients in a micro computed tomography

Critical values of the microstructural parameters at the first critical density of the densification of polar firn

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