Ice-albedo feedback

 

During the summer melt season, the sea ice cover undergoes profound changes in its physical state and optical properties. As the incident solar radiation increases and air temperatures warm, the ice cover evolves from a highly reflective, snow-covered medium to a darker combination of bare ice, melt ponds, and leads. Summer ice melt is controlled by the albedo, which decreases as the melt season progresses in response to a number of positive feedback processes. To understand the ice-albedo feedback mechanism, we must determine how shortwave radiation is distributed within the ice-ocean system and the effects of this distribution on the heat and mass balance of the ice pack. This would be a straightforward task if the ice cover were uniform and homogeneous; a time series of observations at a single point would suffice. However,  the summer ice cover is far from uniform, with surface conditions varying from deep snow to bare ice to melt ponds to open leads and ice thickness ranging from open water to ridges tens of meters thick, all within an area of less than a km2. All of these categories have significantly different physical and optical properties, each processes the incident shortwave irradiance differently, and each has its own particular heat and mass balance that responds differently to similar thermal forcing.
The ice-albedo feedback is an easy concept to understand. The snow-covered sea ice reflects most (>80%) of the incident sunlight, but some is absorbed. This absorbed sunlight leads to melting, which in turn lowers the albedo, resulting in more absorbed sunlight, increasing melting, and lowering the albedo even more... This is a straightforward positive feedback mechanism. While we can describe it qualitatively, a quantitative understanding is lacking. Quantitatively understanding the ice-albedo feedback mechanism is a central goal of SHEBA.  

 

 

What is the albedo in these two scenes and how does it evolve temporally ?

April 1998

July 1998

 

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