The archived Sea Ice Index data are numbers and images representing Arctic- or Antarctic-wide monthly sea ice extent, concentration, and anomolies. These numbers and images are derived from passive microwave satellite data as described in the documentation. Daily images are not archived but daily data are, however, there is day-to-day variability that can reflect instrument or processing errors. Thus, the monthly data products are a more reliable record of ice variability. Here you can access the monthly Sea Ice Index archives of images and data in various formats.
Only monthly image files are available in the archive. To access the images, go to the FTP directory and choose a month directory (indicated by a 3-character month abbreviation). The files are named H_yyyymm_type.png, where H stands for the hemisphere (N or S), yyyy is the 4-digit year, mm is the 2-digit month, and type is the type of image in the file: extent (extn), concentration (conc), concentration anomalies (anom), and concentration trends (trnd). For example, the file S_200303_anom.png is an image of concentration anomalies in the Southern Hemisphere in March 2003.
The ASCII data files tabulate extent and area (in millions of square kilometers) by year for a given month. To access the files, go to the FTP directory and choose a month directory (indicated by a 3-character month abbreviation). The files are named N_mm_area.txt (Northern Hemisphere) and S_mm_area.txt (Soutern Hemisphere) where mm is the 2-digit month. For example, the file N_04_area.txt contains data from the Northern Hemisphere for the month of April.
Monthly sea ice extent shapefiles, November 1978 to present. Shapefiles are available for Northern and Southern hemispheres, both polygons and polylines.
Monthly median shapefiles. Each month's shapefile indicates that month's median extent for the period 1979 to 2000. Shapefiles are available for Northern and Southern hemispheres, polylines only.
To access the files, go to the FTP shapefiles directory and choose a month directory (indicated by a 3-character month abbreviation). Shapefiles are organized in monthly directories, by extent for that month and year or by median extent for that month. Files are zipped. For example, extent_N_199806_polyline.zip contains the polyline extent shapefile for the Northern Hemisphere for June 1998.
These files provide the total extent for each day for the entire time period. There are two data files for each hemisphere: a final and a near-real time. The final file uses data processed at NASA Goddard that goes through manual quality control as input values. However, these data are not available on a near-real-time basis, so a near-real-time file is provided that provides data up to the present. The data in the near-real-time file are the data that are in the Daily Total Sea Ice Extent Time Series Graphs. The data files are in comma delimited ASCII text format (.csv). For more information on how these are processed, see the Daily Total Extent Data Files section of the Sea Ice Index documenation.
These files contain the data for the solid grey line and the light grey standard deviation swath in the Daily Total Sea Ice Extent Time Series Graph. The data files are in comma delimited ASCII text format (.csv). For more information on how these are processed, see the Climatology Data Files section of the Sea Ice Index documenation.
The Sea Ice Index is derived from the following data sets:
These satellite-derived images depict current sea ice conditions and trends. Long-term changes in Arctic sea ice are an index of climate change. Southern Hemisphere sea ice images are also available. For more information about current conditions and their significance, see Arctic Sea Ice News and Analysis.