SEA ICE abstract climate sea ice influences Earth's temperature and deep ocean circulation global distribution there are major differences between north and south polar sea ice concentrations formation sea ice formation types descriptions and definitions drift and deformation wind and water make sure that sea ice is constantly in motion  satellite detection the advent of satellite microwave radiometry changed our view of polar sea ice  references    Researched and written by Ron Merritt Morris       ABSTRACT

       Sea ice is a high latitude phenomenon that influences climate by modifying exchanges between the atmosphere and ocean and by redistributing heat and freshwater.  Deep ocean circulation is driven by the cold, dense waters that are partially created and ventilated by sea ice formation and other high latitude processes. Local temperature extremes are also mediated by the heat fluxes of sea ice formation and decay.
        At any given time, the coverage of global sea ice extends over an area larger than the North American continent.  Its extent fluctuates at each pole, strongly tied to the seasonal intensity of the incoming solar radiation.  Sea ice cover typically consists of broken ice sheets, called floes, that drift large distances under the influences of oceanic and atmospheric forces. The sea ice in the Northern Hemisphere extends into the middle latitudes due to the effect of continentality and maintains a persistent and thick cover over most of the Arctic Ocean basins even though half of all north polar ice melts during the warmer months. About 80% of the Southern Hemisphere's sea ice melts during the summer and its growth is confined to the high latitudes due to the relatively warm ocean surrounding its northward extent.
          The surface mixed layer must achieve subzero temperatures before sea ice begins to form.  The density of subzero waters is greatly salinity-dependent and therefore a small freshening in the surface waters inhibits convection and maintains a "lid" on subsurface heat, allowing the surface mixed layer to cool to freezing temperatures.  As sea ice forms, its crystals aggregate into sizable chunks and it progresses through a series of ice types before it eventually freezes into sheets approximately 2 meters thick.  Its thickness can be increased, if it survives the first year, to 3 meters, but does not typically achieve even greater thicknesses unless local forces cause ice ridging and rafting.
        The polar regions have proven to have formidable conditions within which to explore and conduct scientific research.  Sea ice has been especially difficult to analyze in terms of regional changes in concentration and extent. Satellite imagery provided our first comprehensive view of regional sea ice behavior, but it wasn't until the advent of passive microwave satellite radiometry that our view attained detailed temporal resolution.  Satellites can now take advantage of the difference in microwave emmissivities between open water and sea ice to detect changes in sea ice concentration on the scale of tens of kilometers.
        The accurate detection of sea ice formation and distribution characteristics are necessary to understand the role sea ice plays in influencing the oceanic and atmospheric controls upon regional climates and oceanic circulation.

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