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NSIDC provides this data set to aid investigations of variability and trends in sea ice cover. Ice cover in these data are indicated by sea ice concentration: the percentage of the ocean surface covered by ice. The ice-covered area indicates how much ice is present; it is the total surface area of a pixel multiplied by the ice concentration in that pixel. Ice persistence is the percentage of months over the data set time period that ice existed at a location. The ice extent indicates whether ice is present; here, ice is considered to exist in a pixel if the sea ice concentration exceeds 15 percent. This data set provides users with data about total ice-covered areas, sea ice extent, ice persistence, and monthly climatologies of sea ice concentrations.
This is the most recent version of these data.
Changes to this version include:
COMPREHENSIVE Level of Service
Data: Data integrity and usability verified; data customization services available for select data
Documentation: Key metadata and comprehensive user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services
|
Geographic Coverage |
Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.
As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.
Stroeve, J. and W. N. Meier. 2018. Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS, Version 3. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/IJ0T7HFHB9Y6. [Date Accessed].NSIDC provides this data set to aid investigations of variability and trends in sea ice cover. Ice cover in these data are indicated by sea ice concentration: the percentage of the ocean surface covered by ice. The ice-covered area indicates how much ice is present; it is the total surface area of a pixel multiplied by the ice concentration in that pixel. Ice persistence is the percentage of months over the data set time period that ice existed at a location. The ice extent indicates whether ice is present; here, ice is considered to exist in a pixel if the sea ice concentration exceeds 15 percent. This data set provides users with data about total ice-covered areas, sea ice extent, ice persistence, and monthly climatologies of sea ice concentrations.
Along with one historical data file from the Electrically Scanning Microwave Radiometer (ESMR), these data are derived from the Scanning Multichannel Microwave Radiometer (SMMR), the Special Sensor Microwave/Imager (SSM/I), and the Special Sensor Microwave Imager/Sounder (SSMIS).
Daily Arctic and Antarctic ice-covered area and total sea ice extent ASCII text data files list the total ice-covered area (km2) and total sea ice extent (km2) for both the Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS and/or the NASA Team Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data algorithms.
Monthly mean sea ice concentrations were used to derive monthly extents for both the NASA Team and Bootstrap algorithms.
The total ice-covered area and sea ice extent data are used to create .png images of regional monthly time-series plots of ice-covered areas, area anomalies, ice extent, and extent anomalies for both the NASA Team and Bootstrap algorithms. The scientific basis for these algorithms and their validation are discussed in Parkinson and Cavalieri (2012), Cavalieri and Parkinson (2008), and Parkinson et al. (1999).
Monthly climatologies of ice persistence binary data files with corresponding .png images are intended for users interested in persistence of ice over a particular month during the time series, which includes January 1979 through current processing. Ice persistence fields provide information on how frequently ice occurs in a region during a given month over the time period of the data. The ice extent climatologies are derived each month from monthly-averaged sea ice concentrations using the NASA Team data.
Monthly sea ice concentration climatology binary data files with corresponding .png images represent mean ice concentration for each month over the entire time period of January 1979 through current processing. The data are derived from the NASA Team data.
Data are provided in the following formats:
Total Ice-Covered Areas and Sea Ice Extent
ASCII text
PNG browse
Ice Persistence
Two-byte integer binary
PNG browse
Monthly Climatology of Sea Ice Concentration
Flat, one-byte integer binary
PNG browse
Data are available at:
https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0192_seaice_trends_climo_v3/
This main directory contains three folders:
ice-persistence/ - Contains monthly climatologies of ice persistence binary data files and a browse/ folder with corresponding .png images of monthly ice persistencemonthly-climatology/ - Contains monthly sea ice concentration climatology binary data files and a browse/ folder with corresponding .png images of monthly climatologiestotal-ice-area-extent/ - Contains three sub folders:
bootstrap/ - Contains ASCII text data files and a browse/ folder with .png files of regional graphs showing monthly time-series plots of ice-covered area, area anomalies, ice extent, and extent anomaliesesmr-smmr-ssmi-merged/ - Contains ASCII text data files of daily and monthly sea ice extent summaries from 01 January 1972 to 31 December 2002 for the Northern Hemisphere and 01 January 1973 to 31 December 2002 for the Southern Hemispherenasateam/ - Contains ASCII text data files and a browse/ folder with .png files of regional graphs showing monthly time-series plots of ice-covered area, area anomalies, ice extent, and extent anomalies
Files are named according to the following conventions:
Convention: persistence.mmm.1979-yyyy.h
Example: persistence.apr.1979-2015.n
where:
| Variable | Description |
|---|---|
persistence |
Identifies this as an ice persistence data file |
mmm |
3-character month abbreviation |
1979 |
First year for which data are available |
yyyy |
4-digit year of the last year for which data are available |
h |
Hemisphere (n: Northern, s: Southern) |
Convention: mean.mmm.1979-yyyy.h
Example: mean.apr.1979-2015.n
where:
| Variable | Description |
|---|---|
mean |
Identifies this as a mean ice concentration percentage data file |
mmm |
3-digit month abbreviation |
1979 |
First year for which data are available |
yyyy |
4-digit year of the last year for which data are available |
h |
Hemisphere (n: Northern, s: Southern) |
The following file naming conventions pertain to both the NASA Team and Bootstrap algorithm data files. Data are provided in two different temporal resolutions: daily and monthly.
There are two different types of daily files: ice covered area files and sea ice extent files.
There are six different types of monthly files: ice covered area files, sea ice extent files, ice covered area anomaly files, sea ice extent anomaly files, monthly mean ice covered area files, and monthly mean sea ice extent files.
Monthly anomalies of ice-covered area and ice extent are calculated from monthly mean ice concentrations throughout the period of study. These anomalies show the deviations from the mean monthly values averaged over the entire time series.
Conventions: gsfc.algorithm.xxxx.area.1978-yyyy.h
gsfc.algorithm.xxxx.extent.1978-yyyy.h
gsfc.algorithm.xxxx.anomaly.area.1978-yyyy.h
gsfc.algorithm.xxxx.anomaly.extent.1978-yyyy.hgsfc.algorithm.xxxx.mean.area.1978-yyyy.hgsfc.algorithm.xxxx.mean.extent.1978-yyyy.h
where:
| Variable | Description |
|---|---|
gsfc |
Indicates that data were acquired from Goddard Space Flight Center (GSFC) |
algorithm |
Algorithm used to process the data (nasateam or bootstrap) |
xxxx |
Indicates that this file is either daily or monthly |
anomaly |
Indicates that this file contains the difference between the monthly data (area or extent) and the total monthly mean for the entire temporal coverage period |
area |
Indicates that this file contains ice-covered area measurements |
extent |
Indicates that this file contains sea ice extent measurements |
1978 |
First year for which data are available |
yyyy |
4-digit year of the last year for which data were available |
h |
Hemisphere (n: Northern, s: Southern) |
Data are provided in two different temporal resolutions: daily and monthly.
Conventions: gsfc.nasateam.extent.1972-yyyy.h
gsfc.nasateam.month.extent.1972-yyyy.h
Examples: gsfc.nasateam.extent.1972-2002.n
gsfc.nasateam.month.extent.1972-2002.n
where:
| Variable | Description |
|---|---|
gsfc.nasateam |
Indicates this is GSFC data processed with the NASA Team algorithm |
extent |
Indicates this file contains sea ice extent measurements |
month |
Indicates this file contains monthly averaged data (otherwise daily) |
1972 |
First year for which data are available |
yyyy |
4-digit year (most recent year of processing) |
h |
Hemisphere (n: Northern, s: Southern) |
Data are in ASCII text format arranged in columns as described in Table 5.
| Column | Description |
|---|---|
Year |
4-digit year |
Mon |
1-digit and 2-digit month |
Day |
1-digit and 2-digit day of month |
DOY |
3-digit day of year |
Ver |
Version number of input NASA Team or Bootstrap data (pre: preliminary, v01: version 01, v02: version 02) |
Region |
The remaining columns of the Arctic and Antarctic daily area and daily extent files list the total ice-covered area (km2) and total sea ice extent (km2), respectively. The columns are labeled by region. Refer to Table 6 and Table 7 for a list of abbreviations for column names. |
The following tables list the Arctic and Antarctic regions covered by this data set and define the abbreviations in the data files.
| Arctic Region | Abbreviation |
|---|---|
| Total Arctic | TotalArc |
| Seas of Okhotsk & Japan | Okhotsk |
| Bering Sea | Bering |
| Hudson Bay | Hudson |
| Baffin Bay | Baffin |
| Greenland Sea | Grnland |
| Kara and Barents Seas | BarKara |
| Arctic Ocean | ArctOcn |
| Canadian Archipelago | CanArch |
| Gulf of St. Lawrence | StLawr |
| Antarctic Region | Abbreviation |
|---|---|
| Total Antarctic | TotalAnt |
| Weddell Sea | Weddell |
| Indian Ocean | Indian |
| Pacific Ocean | Pacific |
| Ross Sea | Ross |
| Bellingshausen and Amundsen Seas | BellAm |
Data are in ASCII text format arranged in columns as described in Table 8 and Table 9 for the daily and monthly data.
| Column Number | Description |
|---|---|
| 1 | 4-digit year |
| 2 | 1-digit and 2-digit month |
| 3 | 1-digit and 2-digit day of month |
| 4 | 1-digit to 3-digit day of year |
| 5 | Observed/interpolated sea ice extent (106 km2) |
| Column | Description |
|---|---|
Year |
4-digit year |
Months (remaining 12 columns) |
3-character month abbreviation |
File sizes vary, but generally are:
N: -39.23, S: -90, E: 180, W: -180
N: 90, S: 30.98, E: 180, W: -180
25 km x 25 km
Arctic: NSIDC Sea Ice Polar Stereographic North
Antarctic: NSIDC Sea Ice Polar Stereographic South
For the Northern Hemisphere, the grid size is 304 x 448 pixels.
For the Southern Hemisphere, the grid size is 316 x 332 pixels.
The temporal coverage for this data set is 26 October 1978 to 31 December 2018.
Parameters include:
The ice persistence data indicate the historical frequency of the presence of ice with at least 15 percent concentration in each pixel of the 25 km polar stereographic grid in binary format.
Northern Hemisphere binary files are 304 x 448 bytes.
Southern Hemisphere binary files are 316 x 332 bytes.
Table 10 lists the data values for the ice persistence files.
| Value | Description |
|---|---|
| 0 | Water, no ice |
| 1 - 100 | Historical frequency of the presence of ice, as a percentage |
| 253 | Coastlines (land adjacent to water) |
| 254 | Land |
The monthly climatology data give the average sea ice concentration for each polar stereographic pixel. A minimum concentration value of 15 percent is imposed. When concentrations are lower than this, the grid cell is considered to be free of ice.
Northern Hemisphere binary files are 304 x 448 bytes.
Southern Hemisphere binary files are 316 x 332 bytes.
Table 11 lists the data values for the ice persistence files.
| Value | Description |
|---|---|
| 0 | Water, no ice |
| 15 - 100 | Average ice concentration; minimum concentration is 15 percent |
| 251 | Indicates pole hole; no direct satellite observation |
| 253 | Coast (land adjacent to water) |
| 254 | Land |
The daily and monthly total sea ice extent and sea ice area data for specified Arctic and Antarctic regions are displayed in ASCII text tables. Anomalies are also provided, which indicate departures from the long-term averages.
Figures 1 and 2 show Bootstrap sample data images for the Total Ice-Covered Areas and Sea Ice Extent data files.
.png)
Figures 3 and 4 show NASA Team sample data images for the Total Ice-Covered Areas and Sea Ice Extent data files.
Figures 5 through 8 show sample data images of the Sea Ice Persistence data files for both the Northern Hemishphere and Southern Hemishphere.
Note: The following sample data images (Figures 5 through 12) were created using a deprecated version of this data set which only included data through 2015. Therefore, these images are intended as visual examples only and should not be compared to the latest version, which includes data through 31 December 2016.
.png)
Figures 9 through 12 show sample data images of the Monthly Climatology of Sea Ice Concentration data files for both the Northern Hemishphere and Southern Hemishphere.
To view time-series plots of an area, area anomalies, extent, and extent anomalies for each region, click on the colored region area in the maps in Figures 13 and 14. The gridded data files for the regions are on the Polar Stereographic Tools page.
To view graphs for an entire area, visit the Total Arctic or Total Antarctic pages.
These data are derived from the following sources:
In computing the total ice-covered area and ice extent data with both the NASA Team and Bootstrap algorithms, pixels must have an ice concentration of 15 percent or greater to be included. Total ice-covered area is defined as the area of each pixel with at least 15 percent ice concentration multiplied by the ice fraction in the pixel (0.15 to 1.00). Total ice extent is computed by summing the number of pixels with at least 15 percent ice concentration multiplied by the area per pixel; thus, the entire area of any pixel with at least 15 percent ice concentration is considered to contribute to the total ice extent. Anomalies are the difference between the current time period's average value and the long-term average. A positive anomaly indicates that the current period has greater extent or area than the average.
Individual ocean pixels containing a minimum of 15 percent ice cover are summed throughout the time series. The maximum ice persistence value is 100 percent. Each pixel represents the percentage of years for which ice was present during that month. Only the NASA Team algorithm is used to compute these data.
A threshold of 15 percent concentration is applied to the monthly climatology fields. Only the NASA Team algorithm is used to compute these data.
Periods for which there are no available data are described in Table 12.
Monthly anomalies of ice-covered area and ice extent are calculated from monthly mean ice concentrations throughout the period of study. These anomalies show the deviations from the mean monthly values averaged over the entire time series.
| Time Periods | Data Type | Description |
|---|---|---|
| October 1978, December 1987 | Sea ice | Sea ice data are missing for most days, so monthly values are not calculated for these months. |
| January 1988 | Sea ice | January 1988 is missing data for the first half of the month. A value is given for this month, but the value may not represent true monthly mean since the sea ice data are incomplete. |
There is a circular section over the Northern Hemisphere pole known as the pole hole, which is never measured due to orbit inclination. For the purposes of ice extent, pixels under the pole hole are always considered to be at least 15 percent. For total ice-covered area, the pixels under the pole hole are not used. The Southern Hemisphere also has a pole hole, but it does not affect this sea ice data set because there is only land under this hole. For SMMR, the hole is 611 km in radius and is located poleward of 84.5 degrees North. For SSM/I and SSMIS, the hole is 311 km in radius and is located poleward of 87.2 degrees North.
For information regarding the sensors used for this product, refer to the SMMR, SSM/I, and SSMIS Sensors page.
Table 13 provides a summary of the version history of this product.
| Version | Date Implemented | Description of Updates |
|---|---|---|
| Version 3.1 | 26 February 2019 |
Changes to this version include:
|
| Version 3 | 06 April 2018 |
Changes to this version include:
|
| Version 2 | 01 January 2017 |
Changes to this version include:
|
| Version 1 | 28 July 2014 |
No science changes were made during this update. |
| 04 September 2013 |
Changes included in this update are:
|
|
| 2004 | Initial release of this data product. |
The climatology presents a summary of the long-term record of satellite-derived sea ice concentrations calculated using the NASA Team (NT) and Bootstrap (BT) algorithms. Prior to this update, the climatology included NT and BT data from 1978 through 2015. Because no changes were made to the NT data that were used in the previous version of this product, only small differences due to averaging data from an additional year are expected.
Because the ice persistence and monthly climatology fields are based on the NT data set, there are only small differences. A few grid cells have small changes, but overall there are minimal changes in the ice persistence and monthly climatology fields in both hemispheres for all months.
The NT-derived fields of regional ice extent and areas similarly consist of just the additional year of data; the values through the end of 2015 are unchanged.
The BT-derived fields do show widespread changes because the underlying Bootstrap data have been updated to a new version. While monthly hemisphere-wide areas show average area increases of less than 2%, some smaller regions—for which even small changes in ice area can be a large percentage of the region’s total—can show much larger percentage changes.
While monthly hemisphere-wide areas show average area increases of less than 2%, some smaller regions–for which even small changes in ice area can be a large percentage of the region’s total–can show much larger percentage changes.
The updated Sea Ice Trends and Climatologies data are consistent in format and value with the previous version and can be used for the same purposes. Because the Bootstrap data have been updated for the entire time series, users of the Bootstrap data should update those applications with the entire Bootstrap data set.
In the Northern Hemisphere, very small differences in sea ice extent were found: less than 0.2 percent for the NASA Team algorithm and less than 0.05 percent for the Bootstrap algorithm.
Differences in Northern Hemisphere sea ice area were also small. Most years had less than 0.05 percent. Differences in the Bootstrap sea ice area were generally less than 0.01 percent.
For both the Bootstrap and NASA Team algorithms, the differences in the Southern Hemisphere were negligible.
These small differences are found in the persistence and monthly climatology data also. The Northern Hemisphere monthly fields showed no difference in 95-98 percent of the sea ice values, and fewer than 0.02 percent of pixels had differences in ice concentration of greater than 2 percent.
Data are now available through 31 December 2013 for all Sea Ice Trends and Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS data sets.
Reprocessing is complete and updated data are now available through 31 December 2012 for all Sea Ice Trends and Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS data sets. With this update, the following changes have been implemented:
The cutoff value which defines a region as ice-covered or not ice-covered has been adjusted from 14.8 percent to 15 percent to more closely match the methodology used to calculate other sea ice extent and area products at NSIDC.
The ocean mask files and maximum extent mask files were removed as they are not the masks used in the production of these data sets.
This most recent reprocessing also rectifies two previous releases of these data sets that contained erroneous data. In January/February of 2012, and May of 2013, the products were to have contained data from 2007 to 2010 and from 2010 to 2011, respectively. However, the climatology products contained data only through 2007. We recommend replacing previously downloaded 2010 and 2011 climatology data files with the climatology files that now extend through 2012. The Total Ice-Covered Area and Extent data set did contain post-2007 data, but reprocessed data utilizing the new methodology are available in the 2012 release.
Julienne Stroeve
Polar Observation & Modelling
University College London
Walt Meier
National Snow and Ice Data Center
January 2017
April 2018
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