Wind alters snow crystals, impacting climate models

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In the Alps, snow transported by the wind often forms snow slabs. Credit: Christian Rixen

Wind tunnel experiments conducted by the WSL Institute for Snow and Avalanche Research SLF show how snow crystals change in the wind. The findings could force climate researchers to adjust their models—particularly in the polar regions, where snow transport by strong winds is widespread.

When snow particles are picked up and blown about by strong winds, they are not only mechanically reshaped by crumbling and grinding. The water also changes between solid and gaseous forms, as experiments in a wind tunnel have shown. Some of the snow changes from the solid to the gaseous phase and is thus returned to the atmosphere in a process called sublimation. In particularly dense "snow transport clouds," however, so-called resublimation can also occur: snow crystals absorb water vapor from the surrounding area and continue to grow.

This to and fro leaves a trace, namely in the composition of the water isotopes in the crystals. These are forms of water molecules of different masses that researchers can detect. Solid, liquid or gaseous water contains different amounts of heavy and light isotopes. So when ice crystals dissolve in gas or form new ones, the ratio of heavy to light isotopes changes, something researchers call fractionation. Isotopes have proven their worth in the analysis of a wide range of processes in the hydrological cycle and also in the atmospheric water cycle.

Wind drives snow over the snow cover. Credit: Beate Kittl, Michael Lehning

Climate record in ice cores

This new finding has implications for the interpretation of ice cores and global climate models, as SLF researchers report in the journal The Cryosphere. The ice in polar ice cores is hundreds of thousands of years old. Climate researchers use isotope analyses to reconstruct past temperatures, integrate them into their climate models and learn something about our climatic future.

Until now, they assumed that the isotopic composition in ice cores directly reflects historical temperature at the time of the snowfall. The discovery could challenge this assumption because resublimation changes the isotopic ratio.

In the Antarctic, the wind shifts enormous amounts of snow, thereby influencing the water balance of this zone, which is important for the global climate. Credit: Hendrik Huwald

The largest water reservoirs on Earth are the polar ice caps. The fact that the wind not only shifts huge amounts of snow there but also transfers it between the ground and the atmosphere through sublimation and resublimation has a major influence on the water balance of the ice masses.

The new findings could help to improve predictions of the water exchange and thus of the climate in polar regions. The researchers are therefore planning to study the newly discovered phenomenon in greater depth and integrate it into climate models.

More information: Sonja Wahl et al, Identifying airborne snow metamorphism with stable water isotopes, The Cryosphere (2024). DOI: 10.5194/tc-18-4493-2024

Journal information: The Cryosphere

Provided by Swiss Federal Institute for Forest, Snow and Landscape Research WSL