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Sea Ice Index

July 1, 2013: The Sea Ice Index team has replaced the
22-year base period with a new 30-year version. Read more.

Sea Ice Index Data and Image Archive

Here you can access the archived monthly and daily Sea Ice Index images and data as well as the input data that the Sea Ice Index is derived from.

All archived data reside in the following FTP location: ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/

The Sea Ice Index archive contains the following:

  • Monthly images of extent, concentration, anomalies, and trends from November 1978 through last month.
    Note: Daily images are not archived, however, the most recent daily image can be obtained from the Sea Ice Index Web page.
  • Monthly sea ice extent and area data files.
  • Monthly GIS compatible shapefiles of ice extent.
  • Daily sea ice extent data files and daily climatology data files with data from November 1978 through yesterday.

Monthly Extent and Concentration Images

Only monthly image files are available in the archive. Daily images are not archived.

Access files:

  1. Go to the FTP directory.
  2. Choose the month directory (indicated by a 3-character month abbreviation) for the data that you are interested in.
  3. Within the month directory, search for the year and type of monthly image files that are named according to the following convention:
    H_yyyymm_type.png
    Where H stands for the hemisphere: N (north) or S (south), yyyy is the 4-digit year, mm is the 2-digit month, and type is the type of image in the file: extn (extent), conc (concentration), anom (concentration anomalies), and trnd (concentration trends).
    For example, the file N_200303_anom.png contains concentration anomalies for the Northern Hemisphere for March 2003.

GIS Compatible Files (shapefiles)

Monthly Extent Shapefiles

Shapefiles are available for Northern and Southern hemispheres, for November 1978 to present, 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.

Access files:

  1. Go to the FTP shapefiles directory.
  2. 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.

Google Earth Files (.kmz)

Compare satellite images of September sea ice minimum extents for the last thirty years for both the Arctic and the Antarctic.

September sea ice extent, 1979 - present (KMZ, 343 KB)

View Arctic and Antarctic sea ice extents from 1979 through present for the months March (maximum sea ice extents) and September (minimum sea ice extents). Note: September is the default month when the file is opened. To see March, click on the March layer in the Google Earth side panel.

Minimum and Maximum Sea ice extents, 1979 - present (KMZ, 1.8 MB)

Monthly Sea Ice Extent and Area Data Files

The ASCII data files tabulate extent and area (in millions of square kilometers) by year for a given month.

Access files:

  1. Go to the FTP directory.
  2. Choose the month directory (indicated by a 3-character month abbreviation) for the data that you are interested in. Within the month directory, search for data files that are named according to the following convention:
    H_mm_area.txt
    Where H stands for the hemisphere: N (north) or S (south), and 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.

Daily Sea Ice Extent Data Files

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 documentation.

Access files:

Daily Climatology Data Files

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 documentation.

Access files:

Passive Microwave Sea Ice Concentrations

These data are not part of the Sea Ice Index archive. They are the input data that the Sea Ice Index is derived from. To access these data and learn more about them, see the following links: