Beyond Point Measurements: Sea Ice Floes Characterized in 3-D

A new methodology for coincident floe-scale measurements of the surface elevation, snow depth, and ice draft (the thickness below the water line) of Antarctic sea ice has been demonstrated during two recent research voyages: the Australian-led Sea Ice Physics and Ecosystem Experiment II (SIPEX II) to East Antarctica in September–November 2012 and the United Kingdom–led Ice Mass Balance in the Bellingshausen Sea (ICEBell) voyage to the Weddell and Bellingshausen Seas in November 2010

LES modeling of wind over Antarctic snow-ice formations using a dynamic surface roughness approach.

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

Wind surface drag over sea-ice is a primary control on sea-ice flow patterns and deformations at scales that are important for climate and weather prediction models. Here, we perform a series of Large Eddy Simulations (LES) of fully developed flow over high-resolution snow-ice surfaces of Antarctic sea ice floes to study surface drag and roughness parameters at process scales from 1 cm to 100 m. Snow/ice surface morphology was obtained using a Terrestrial Laser Scanner during the SIPEX II (Sea Ice Physics and Ecosystem experiment II) research voyage to East Antarctica (September-November 2012). LES are performed on a regular domain adopting a mixed pseudo-spectral/finite difference spatial discretization. A scale-dependent dynamic subgrid-scale model based on Lagrangian time averaging is adopted to determine the eddy-viscosity in the bulk of the flow. The effects of large-scale features of the surface on the wind flow (those features that can be resolved in LES) are accounted for through an immersed boundary method. Conversely, the drag forces caused by subgrid-scale features of the surface should be accounted for through a parameterization. However the effective aerodynamic surface roughness parameter z0 for snow ice is not known. Hence, a dynamic approach is utilized, in which this parameter is determined using the first-principles based constraint that the total momentum flux (drag) must be independent on grid-filter scale. This dynamic surface roughness model is inspired by the Germano identity, traditionally used to determine model parameters for closing subgrid-scale stresses in the bulk of a turbulent flow. This type of model has been previously applied to flow over multi-scale terrain and ocean waves but never for snow-ice surfaces. The resulting dynamic parameter will be compared with values obtained for solid terrain and ocean sea surface values, and the implications on overall drag forces on snow ice surfaces will be discussed.

2013

Spatially-resolved mean flow and turbulence help explain observed erosion and deposition patterns of snow over Antarctic sea ice

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

Sea ice-atmosphere interactions are major drivers of patterns of sea ice flows and deformations in Polar regions, and affect snow erosion and deposition at the surface. Here, we combine analyses of sea ice surface topography at very high-resolutions (~1-10 cm), and Large Eddy Simulations (LES) to study surface drag and snow erosion and deposition patterns from process scales to floe scales (~ 1 cm – 100 m). The snow/ice elevations were obtained using a Terrestrial Laser Scanner during the SIPEX II (Sea Ice Physics and Ecosystem eXperiment II) research voyage to East Antarctica (September-November 2012). LES are performed on a regular domain adopting a mixed pseudo-spectral/finite difference spatial discretization. A scale-dependent dynamic subgrid-scale model based on Lagrangian time averaging is adopted to determine the eddy-viscosity in the bulk of the flow. Effects of larger-scale features of the surface on wind flows (those features that can be resolved in the LES) are accounted for through an immersed boundary method. Conversely, drag forces caused by subgrid-scale features of the surface should be accounted for through a parameterization. However, the effective aerodynamic roughness parameter z0 for snow/ice is not known. Hence, a novel dynamic approach is utilized, in which z0 is determined using the constraint that the total momentum flux (drag) must be independent on grid-filter scale. We focus on three ice floe surfaces. The first of these surfaces (October 6, 2012) is used to test the performance of the model, validate the algorithm, and study the spatial distributed fields of resolved and modeled stress components. The following two surfaces, scanned at the same location before and after a snow storm event (October 20 and 23, 2012), are used to propose an application to study how spatially resolved mean flow and turbulence relates to observed patterns of snow erosion and deposition. We show how erosion and deposition patterns are correlated with the computed stresses, with modeled stresses having higher explanatory power. Deposition is mainly occurring in wake regions of specific ridges that strongly affect wind flow patterns. These larger ridges lock in place elongated streaks of relatively high speeds with axes along the stream-wise direction, and which are largely responsible for the observed erosion.

2014

Analysis of surface drag over Antarctic sea ice from High-Resolution measurements from Terrestrial Laser Scanning and Large Eddy Simulations

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

Sea ice/snow surface interactions with the atmosphere are major drivers of large-scale patterns of sea ice flows and deformations in Polar Regions. Climate and weather prediction models require parameterizations of the subgrid-scale surface drag caused by the interactions between the ice/snow surfaces and surface winds. Here, we combine the analysis of sea ice/snow surface topography at very high-resolutions (~1-10 cm), local wind measurements, and Large Eddy Simulations (LES) of fully developed wind flow to study surface drag and roughness from process scales to floe scales (~ 1 cm – 100 m). The snow/ice elevations were obtained using a Terrestrial Laser Scanner (TLS) during the SIPEX II (Sea Ice Physics and Ecosystem eXperiment II) research voyage to East Antarctica (September-November 2012). LES are performed on a regular domain adopting a mixed pseudo-spectral/finite difference spatial discretization. A scale-dependent dynamic subgrid-scale model based on Lagrangian time averaging is adopted to determine the eddy-viscosity in the bulk of the flow. The effects of large-scale features of the surface on wind flows (those features that can be resolved in the LES) are accounted for through an immersed boundary method. Conversely, drag forces caused by subgrid-scale features of the surface should be accounted for through a parameterization. However the effective aerodynamic surface roughness parameter z0 for snow/ice is not known. Hence, a dynamic approach is utilized, in which this parameter is determined using the first-principles based constraint that the total momentum flux (drag) must be independent on grid-filter scale. LES are performed over fine scans of typical surface structures, and over larger domains filtered at coarser grid resolutions (~ 1 m). A total of six ice floes are studied, with before and after-storm TLS data at one of the floes for an analysis of the changes in the surface structure and its effects on the surface-atmosphere interactions. The spatial distributions of friction velocities (U*), wind profiles, and variations of z0 values along different directions are obtained from the LES for scenarios with variations in wind forcings and predominant wind directions relative to the general alignment of surface features. LES results are compared to spatial statistics of the surface at the locations to determine relationships with the general characteristics of the floes, and analyzing the variations between the different floes studied.

2014

LES modeling of wind over Antarctic snow-ice formations using a dynamic surface roughness approach.

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

2013

Analysis of surface drag over Antarctic sea ice from High-Resolution measurements from Terrestrial Laser Scanning and Large Eddy Simulations

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

2014

Spatially-resolved mean flow and turbulence help explain observed erosion and deposition patterns of snow over Antarctic sea ice

Marco Giovanni Giometto, Michael Lehning, Katherine Colby Leonard, Charles Vivant Ignacio Meneveau, Marc Parlange, Ernesto Trujillo Gomez

2014