US National/Naval Ice Center digital sea ice data and climatology

Weekly sea ice charts produced by the National Ice Center (NIC) from 1972 through 1994 have recently been released to the public in support of environmental research. These charts were originally intended as navigation aids for vessels operating Northern Hemisphere sea ice-infested waters. However, it was recognized early on that these data represent a unique resource for Arctic researchers, adding significantly to sea ice data sets compiled by Walsh (1978) and others. Ice concentration records commonly derived from satellite passive microwave data are similar to the NIC data set in terms of resolution, extent and period of record, but these microwave data may suffer from systematic biases related to the imaging process and algorithms used to infer ice concentration from raw data. Although the NIC digital sea ice data set has its own limitations, its starting point precedes that of the passive microwave record and avoids some of its inherent biases. This paper describes the spatial and thematic characteristics of the NIC historical data set, as well as the digital and analog data and analysis methods used to create the data set. This study, also briefly investigates long-term change in Arctic ice cover. The NIC data set reveals that sea ice concentration patterns in the Atlantic and Pacific sectors of the Arctic vary in response to changes in the North Atlantic Oscillation. This result is consistent with the findings of other researchers, who used other data sets.