Impact of crevasses on surface energy balance at an alpine glacier

Observations worldwide have shown that glaciers are receding. Thinning snow cover can result in crevasses becoming exposed at the glacier surface for longer time periods. Crevasses can increase surface roughness, change the surface wind flow fields, and impact the air temperatures within and outside the crevasses (Purdie et al., 2022). Therefore, more can be learnt about regarding the impact of crevasses on energy exchange with glacier atmospheric boundary layer. In order to understand and investigate the atmosphere-crevasse energy exchange, we carried out numerical Large Eddy Simulation (LES) experiments using the PALM model system 6.0 with crevasse-resolving grid spacings less than 1 m. The PALM model system 6.0 has been used for atmosphere and marine boundary layer studies to understand complex processes of atmospheric dynamics and energy balance. Our preliminary results show that the air inside a crevasse does not cool as fast as the air outside a crevasse resulting in net warming from the crevasse relative to the glacier surface. These results agree with the field study conducted at Tasman Glacier (Purdie et al., 2022), and confirm that crevasses could lead to heat storage and increased melting. During the daytime, air temperature inside a crevasse could be 1 °C higher than the air above the glacier surface. After sunset, the presence of the crevasse entrains and traps the warm air such that the centre of the crevasse could still be warmer than the glacier surface during the first half of the evening.  During windy evenings, our results show that turbulent heat exchange associated with eddy entrainment leads to exchange of air mass between the crevasse and the glacier surface, which then causes glacier surface warming. Our preliminary simulations only included one crevasse, while future work will include a field of crevasses to investigate the impact of crevasses in a more realistic environment. This study highlights the importance of including crevasses energy balance in glacier modelling, neglecting which would lead to significant bias in snow melt and mass balance estimations.

 

Reference:

Purdie, H., et al. (2022). "Variability in the vertical temperature profile within crevasses at an alpine glacier." Journal of Glaciology: 1-5.