Giant ice sheets in Greenland and Antarctica are melting. The faster the earth warms, the faster the sea level rises due to a large amount of meltwater.
It turns out that the properties of drifting snow also play a role in this. Not only does drifting snow slow the growth of ice sheets, it also affects the wind that blows over the polar ice caps.
Antarctica - (Image Credit: Artsiom P via Shutterstock / HDR tune by Universal-Sci)
Drifting snow is a two-phase flow
Drifting snow belongs to the so-called two-phase flows, in which a flowing medium (air) and particles (snowflakes) move together and influence each other.
Other examples of two-phase flows are sediment transport (clay, sand) in rivers and in the sea, dust storms on Mars, and sea spray. Drifting snow is one of the few two-phase flows where particles constantly change size via sublimation (ice turning into water vapor).
The wind is slowed down close to the ground by friction. The rougher the surface, the stronger the inhibition (which is why the wind blows harder over the sea than over land). The special thing about drifting snow is that it makes a smooth surface feel rough.
The amount of drifting snow decreases very sharply with altitude. The main reason for this is that large and heavy particles stay close to the surface. In saltation (the bottom few centimeters), particles bounce off the surface.
Image Credit : AlexDreamliner via Shutterstock
Lifting snow particles costs energy. As a result, the wind encounters strong friction near the surface, which is comparable to the friction caused by a rough surface. During drifting snow, the so-called roughness length (a measure of the surface's roughness) increases sharply with wind speed (and thus with the amount of drifting snow). This effect has been clearly reflected in wind measurements on the Antarctic ice sheet.
Making snow particles float costs energy
As wind speed increases, snow particles float (as they are carried along with the current); this is called suspension. During suspension, snow particles are propelled upwards by vortices in the wind, while gravity pulls them downwards at the same time.
Depending on the size and weight of the particle as well as wind speed, the particle reaches a certain average height. The wind continuously supplies energy to keep the snow particle afloat and therefore decreases in strength.
Because most and heaviest particles reside close to the surface, the weight of the drifting snow-filled air decreases sharply with height. This means it takes a lot of energy to lift relatively heavy air containing drifting snow. Drifting snow thus provides firm damping of the wind.
Thus, both saltation and suspension act in different ways to dampen the wind, an effect significant enough to play a role in the development of large icecaps.
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