Seasonal and Regional Variations of Northern Hemisphere Sea Ice as Illustrated with Satellite Passive-Microwave Data For 1974

Abstract

A detailed description of the seasonal cycle of Northern Hemisphere sea ice for 1974 is provided by the passive microwave data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR). Sea ice extent has been mapped and analyzed in eight regions of the Arctic and marginal seas. In the seasonal sea ice areas, the ice concentration is also mapped, whereas in areas of first-year and multiyear ice mixtures, the corresponding mapping is of a parameter representing a combination of ice concentration and multiyear ice fraction. The total monthly ice extent increased from a sharp minimum of 7.6 × 106 km2 in September, when the ice pack was mostly confined to the central Arctic Ocean and portions of the Greenland Sea, Kara Sea, and Canadian Archipelago, to a broad maximum of 14.4 × 106 km2 in March, when the ice cover was nearly complete in the Arctic Ocean, Hudson Bay, Kara Sea, and Canadian Archipelago and was extensive for large portions of the other peripheral seas and bays. In the areas of seasonal sea ice coverage, the average ice concentration was approximately 75% in winter, which is close to the values observed in the Southern Ocean and significantly less than the greater-than-95% concentrations observed in the central Arctic Ocean and Hudson Bay, where the ice packs are constrained by land boundaries. Midwinter decreases in ice extent for 1—2 months are noted in the regions of the Greenland Sea and the Kara and Barents Seas.