Local surface mass balance processes in East Antarctica

In Antarctica, direct observations of key processes shaping the surface mass balance such as precipitation and snow deposition, wind transport of snow, and sublimation, are sparse due to the extreme environment and related difficulties in measuring the variables of interest. The ongoing project ‘Local Surface Mass Balance in East Antarctica’ (LOSUMEA) is designed to address these processes at the local scale with the objective of gaining insight on the dominant surface mass and energy balance components and their link to near-surface atmospheric dynamics and surface and sub-surface snow properties. To this end, two measurement stations have been installed near the Princess Elisabeth Station, Antarctica, in December 2016. Besides standard meteorological data the stations are equipped with snow particle counters and 3-D sonic anemometers relating wind, turbulence and mass flux. Pre- and post-storm Terrestrial Laser Scans (TLS) record the resulting surface morphological changes. While preliminary data is being analyzed, the full data set of the year 2017 is retrieved in early 2018. Addition of moisture sensors in 2018 is expected to provide valuable information on latent heat fluxes related to sublimation. This contribution presents an overview of the project experiments, the data obtained to date as well as their analysis and some first results.

Local snow transport and surface evolution processes in East Antarctica

Francesco Comola, Philip Crivelli, Wolf Hendrik Huwald, Michael Lehning, Eric Sauvageat, Varun Sharma, Nander Wever

In Antarctica, direct measurements of processes shaping the surface mass balance such as precipitation, accumulation and erosion, drifting and blowing snow, and sublimation, are sparse and challenging due to the extreme environment and related difficulties in measuring the variables of interest. An ongoing project, ‘Local Surface Mass Balance in East Antarctica’, is designed to address these processes at the local scale with the objective of relating near-surface atmospheric dynamics, drifting and blowing snow, snow properties, and resulting accumulation and erosion patterns. Two snow mass balance stations at Princess Elisabeth, Antarctica, (72S, 23E, 1380m.a.s.l.) are collecting data since December 2016, including standard meteorological instruments, snow particle counters and 3-D sonic anemometers for combined analysis of wind, turbulence and mass flux. Pre- and post-storm Terrestrial Laser Scans (TLS) record the resulting surface morphological changes. This contribution presents analysis and preliminary results of the turbulence and wind data to obtain vertically integrated mass flux estimates. Calculated surface roughness and friction velocities are used for establishing formulations of vertical profiles of drifting and blowing snow. Stability corrections, auto- and cross-correlation functions of wind and mass flux, as well as the lag-time between sonic anemometers and snow particle counters are investigated. It is shown which vertical profile shape leads to consistent mass flux estimates and how magnitudes of calculated mass fluxes compare to earlier estimates. The comparisons suggest that mass transport has rather been underestimated in early and several current studies.

2018

How well do we understand the influence of drifting and blowing snow in extreme environments?

Jérôme François Sylvain Dujardin, Franziska Gerber, Michael Lehning, Varun Sharma, Benjamin Andreas Walter

Extreme cold environments such as the polar regions and high mountain areas are characterised by unknown precipitation quantities and a high variability of snow and ice masses. A key player in understanding the surface mass balance in these areas is drifting and blowing snow. Apart from the surface mass balance, drifting and blowing snow may perturb the surface structure of the boundary layer resulting in feedback loops that have not been sufficiently explored, especially at large scales. In this contribution we review recent advances in measuring and modelling drifting and blowing snow as well as their effects on the atmosphere and the surface mass balance. In particular, we suggest that current models may underestimate drifting snow sublimation because they assume saturation close to the surface and do not adequately represent the effects of transient (turbulent) wind fields. We highlight the importance of knowing not only the frequency of snow transport occurrence but also the height distribution of both mass flux and humidity for an accurate assessment. Therefore, we present first ground-based micro rain radar measurements of blowing snow clouds in Antarctica and show examples of blowing snow events which are not represented in current weather and climate models. Additionally, recent advances made is simulations of blowing snow clouds in Antarctica are present and compared with measurements. These simulations play the critical role of understanding the effect of drifting and blowing snow at continental scale. Results from such simulations, particularly on vapor contribution due to blowing snow sublimation will be presented as examples to highlight their utility.

2019

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

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