E9 Cryosphere-Armosphere Interactions

Topic

The cryosphere interacts with the overlying atmosphere primarily through three channels: the albedo of its icy surfaces, the turbulent fluxes of sensible and latent heat exchanged with the air, and the emission of trace gases into that same air.

The ice-albedo feedback is the most powerful of these three channels: an ice or snow surface reflects between fifty and ninety percent of the incoming solar radiation, whereas the land or ocean exposed when that icy surface disappears reflects only ten to thirty percent of that same radiation. When the cryosphere loses part of its ice cover, a low-reflectivity surface is exposed that absorbs far more solar radiation than the ice cover did; this increased absorption further warms the air and the exposed land or ocean, and this additional warming melts even more ice cover, amplifying the initial warming in a self-reinforcing cycle. This same ice-albedo feedback is responsible for the Arctic amplification observed in polar regions today.

A katabatic wind is a cold, dense wind that descends under the force of gravity from polar plateaus toward the coast; it originates from the intense temperature inversion that forms directly above the cold, icy surfaces of these plateaus. Air in direct contact with the ice cools and becomes denser than the air above it, causing this denser air to flow downslope, driven solely by its own weight. In Antarctica, a katabatic wind can reach speeds of between fifty and one hundred meters per second; at such speeds, it alters the region's sensible heat balance, accelerates snow ablation, and disrupts sea-ice formation along the coast.

Snow also acts as a highly effective thermal insulator between the ground beneath it and the atmosphere above: a snow layer just half a meter thick reduces the heat flux escaping from the ground into the atmosphere by a factor of ten to one hundred compared to bare ground. This insulating effect protects permafrost from extreme winter cold and is crucial for both ecosystems and agriculture in cold latitudes that rely on that permafrost or the underlying soil.

Climate-warming-induced changes to snow cover profoundly alter this insulating effect—and, consequently, the entire seasonal hydrological cycle that depends on the timing of snow accumulation and melt; this is the very cycle of cryosphere-atmosphere interactions with which this description began.

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