As the ice forms seasonally, the growing pack can take on swirl patterns caused by eddy current circulation, as seen in this SIR-C image:

The nature of ice packs in the Arctic over a large area is exemplified by this HCMM Vis image of the Chukchi Sea in the Bering Strait between Alaska and Siberia. The ice in this scene is characterized by a network of cracks, called leads, which open up during summer breakup and refreeze when conditions demand.

Growth or decrease of the ice fields surrounding the Antarctic as sensed by ESMR was pictured earlier in this Section. Changes in ice cover for four years during the 1978-86 period as sensed by SMRR are indicated in the top diagram below. On the bottom is a view of the north polar regions, showing the prevailing ice cover, made by NSCAT (the NASA Scatterometer).

In the U.S. winter ice on the Great Lakes becomes a major impediment to shipping and usually some or all of the lakes are closed to normal travel. The status of ice cover is monitored daily by the AVHRR on NOAA satellites, giving results like this thermal IR image made on January 31, 1996 (ice is light-toned; clouds appear very dark):

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