The Decaying Near‐Surface Boundary Layer of a Retreating Alpine Glacier

• Published in: Geophysical research letters Vol. 50; no. 11
• Main Authors: Shaw, Thomas E., Buri, Pascal, McCarthy, Michael, Miles, Evan S., Ayala, Álvaro, Pellicciotti, Francesca
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-06-2023; Wiley
• Subjects: Air temperature; boundary layer; Boundary layers; Climate change; Enthalpy; Future climates; glacier; Glacier ice; Glacier melting; Glacier retreat; Glacier temperatures; Glacier winds; Glaciers; Global warming; Heat flux; Heat transfer; Katabatic winds; Meteorological data; Mountain glaciers; Sensible heat; Sensitivity; Surface boundary layer; temperature; temperature sensitivity; Valley winds; Valleys; wind; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103043

The presence of a developed boundary layer decouples a glacier's response from ambient conditions, suggesting that sensitivity to climate change is increased by glacier retreat. To test this hypothesis, we explore six years of distributed meteorological data on a small Swiss glacier in the period 2001–2022. Large glacier fragmentation has occurred since 2001 (−35% area change up to 2022) coinciding with notable frontal retreat, an observed switch from down‐glacier katabatic to up‐glacier valley winds and an increased sensitivity (ratio) of on‐glacier to off‐glacier temperature. As the glacier ceases to develop density‐driven katabatic winds, sensible heat fluxes on the glacier are increasingly determined by the conditions occurring outside the boundary layer of the glacier, sealing the glacier's demise as the climate continues to warm and experience an increased frequency of extreme summers.
Plain Language Summary
Down‐glacier winds promote a unique micro‐climate, maintaining relatively lower temperatures over the surface of mountain glaciers. Using six years of meteorological data in the period 2001–2022, we observe increases in the relative changes of above‐ice air temperatures compared to temperatures outside the glacier. As the glacier ceases to develop its own micro‐climate, warmer winds generated by heated valley slopes increasingly control the amount of heat transfer to melt glacier ice. This work offers new observational evidence that suggests that, as glaciers continue to shrink and fragment, they becoming increasingly sensitive to future climate warming.
Key Points
On‐glacier air temperatures have become more sensitive to ambient temperatures in a warming climate
Up‐valley winds have increased >20% between 2001 and 2021, making sensible heat fluxes more dependent on conditions outside the glacier
The decay of the katabatic system due to glacier retreat indicates a nonlinear sensitivity of the glacier to continued warming