Do Windy Glaciers Melt Faster?

The relationship between surface winds and glacial melt is more complex than previously thought, according to an article in the journal, Boundary-Layer Meteorology, which used new data collecting techniques.

The report by Maxime Litt, Jean-Emmanuel Sicart, and Patrick Wagnon, with the Université Grenoble Alpes, France, and, Warren D. Helgason at the University of Saskatchewan, Canada, focused on the tropical Zongo glacier in the mountains of Bolivia. They were able to demonstrate that over mountain glaciers katabatic winds and turbulent heat fluxes, which had not been properly measured in the past, were common with substantial effects on glacial wind, and could have substantial effects on glacial mass.

Katabatic glacial wind blown snow over a mountain peak
Katabatic wind-blown snow caught behind craggy peaks, near Meehan Glacier in NW Greenland. By, NASA/Jeremy Harbeck, via Flicker.

Katabatic winds are a gravity driven wind that occur when air high above the ground is more dense than the air beneath it, causing the air to fall, often down a mountain slope. Glaciers are a common cause of these types of winds because the air directly above the ice is likely to be cooler than the surrounding air at the same altitude, and because cold air is denser, air atop mountain glaciers often falls downhill, creating katabatic winds.

By their nature katabatic winds vary with the temperature of the surrounding air, and for this reason do not occur constantly, nor at consistent speeds. This means that the behavior of katabatic winds depends on the weather and climate surrounding the glacier.

At the same time that strong winds intermittently blow down glaciers, smaller surface anomalies on glaciers and differences in terrain around glaciers cause air that carries heat to become turbulent, creating different turbulent heat fluxes, or the amount and speed with which air and heat get churned up over the surface of the glacier as the wind moves.

As an example, you can think of it as similar to the way farmers will plant wind breaks in their fields to prevent soil erosion. Planting trees and bushes in a field will affect the way that air travels through the field, in this case by preventing strong winds from blowing away top soil.

Figure of effect of wind breaks from the U.S. Department of Agriculture Natural Resources Conservation Service
Figure of effect of wind breaks from the U.S. Department of Agriculture Natural Resources Conservation Service

Much as the way that the amount of wind erosion of soil is affected by surface characteristics (a flat field or a field with a line of trees), the amount of glacier melting and sublimation will be affected by the terrain around the glacier and the characteristics of its surface.

Previously, scientists had used a method of calculating the effect of wind driven melting which did not consider the effects of changing turbulence and intermittent katabatic winds.

On uniform stable surfaces the method previously used, called the “bulk aerodynamic method,” is considered standard. However the researches in this study demonstrated that on mountain glaciers, more precise methods were needed, because of intermittent downhill winds and variability in wind turbulence due to complex terrain features.

Using on-site measuring equipment and a six month long real-world study of the Zongo glacier, the researchers demonstrated that the previously unconsidered winds did contribute to the melting and freezing of the glacier. They suggest  that these types of winds should be considered in future studies of glacial expansion and recession.

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