This data set provides weekly estimates of sea ice age for the Arctic Ocean derived from remotely sensed sea ice motion and sea ice extent. The temporal coverage for this data set is January 1984 through December 2019. For more recent data, see the Quicklook Arctic Weekly EASE-Grid Sea Ice Age data product (https://nsidc.org/data/nsidc-0749).
EASE-Grid Sea Ice Age, Version 4
This is the most recent version of these data.
The input ice motion data used for this data set is now derived from the Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors Version 4 data set. Data files are now provided in netCDF format.
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Geographic Coverage |
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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.
Tschudi, M., W. N. Meier, J. S. Stewart, C. Fowler, and J. Maslanik. 2019. EASE-Grid Sea Ice Age, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/UTAV7490FEPB. [Date Accessed].Data Description
Parameters
The main parameter for this data set is sea ice age, measured in years.
File Information
Format
Data are provided in georeferenced netCDF (.nc) format.
PNG (.png) browse images are also provided.
File Contents
Each netCDF file contains 52 weeks of sea ice ages, coded as integers in a 722 x 722 gridded subset of the 12.5 km Northern Hemisphere EASE-Grid. Table 1 lists the coded integer values and their meanings.
Value
|
Description
|
---|---|
0
|
Open water or < 15% sea ice concentration
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1, 2, 3, ..., 16
|
Sea ice age; higher age estimates are not precise, so older ice, 5th-year (4-5 years old) and above, are generally considered together
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20
|
Designates the grid cell contains only land
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21 | Designates grid cells that contain ocean for which ice age was not calculated |
Sample Browse Image
One browse image displaying sea ice age is provided for every week of data. Figure 1 shows a sample browse image.

Directory Structure
Data are available for download via HTTPS; the link is accessible through the "Download Data" tab. Within the file directory, there are two folders, data
and browse
. The data
folder contains the sea ice age netCDF files, while the browse
folder contains the PNG browse images, which are further subdivided into folders by year.
NetCDF File Naming Convention
The data files are named according to the following convention and as described to Table 2:iceage_hh_rrrr_<start-date>_<end-date>_v##.nc
Example:
iceage_nh_12.5km_19840101_19841231_v4.1.nc
Variable | Description |
---|---|
hh | Hemisphere (nh = Northern) |
rrrr | Resolution of input data source in km (e.g. 12.5 km) |
<start-date> | First day of data contained in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
<end-date> | Last day of data contained in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
v## | Version number |
Browse Image File Naming Convention
The browse images are named according to the following convention and as described to Table 3:iceage_hh_rrrr_<start-date>_<end-date>_v##.png
Example:iceage_nh_25km_20000101_20000107_v4.1.png
Variable | Description |
---|---|
hh | Hemisphere (nh = Northern) |
rrrr | Gridded spatial resolution (e.g. 12.5 km) |
<start-date> | First day of the week that the image represents, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
<end-date> | Last day of the week that the image represents, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
v## | Version number |
File Size
NetCDF files are approximately 3.5 - 4.0 MB.
Browse images are approximately 400 KB.
Spatial Information
Coverage
This data set covers the Arctic Ocean within the boundaries defined below:
Southernmost Latitude: 48.4° N
Northernmost Latitude: 90.0° N
Westernmost Longitude: 180.0° W
Easternmost Longitude: 180.0° E
Resolution
12.5 km
Geolocation
Data are projected using a 12.5 km Northern Hemisphere EASE-Grid. The grid is shifted one-half grid cell relative to the standard version of EASE-Grid, which have the center of the grid right over the pole. More details can be found in tables 4 and 5 below. More details on EASE-Grid can be found on the EASE Grids website.
Geographic coordinate system | N/A |
---|---|
Projected coordinate system | NSIDC EASE-Grid North |
Longitude of true origin | 0 |
Latitude of true origin | 90 |
Scale factor at longitude of true origin | N/A |
Datum | N/A |
Ellipsoid/spheroid | International 1924 Authalic Sphere |
Units | meter |
False easting | 0 |
False northing | 0 |
EPSG code | 3408 |
PROJ4 string | +proj=laea +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +a=6371228 +b=6371228 +units=m +no_defs |
Reference | http://epsg.io/3408 |
Grid cell size (x, y pixel dimensions) |
12534 projected meters (x)
12534 projected meters (y) |
---|---|
Number of rows | 722 |
Number of columns | 722 |
Geolocated lower left point in grid | 29.7° N, 45.0° W |
Nominal gridded resolution | 12.5 km by 12.5 km |
Grid rotation | N/A |
ulx – x-axis map coordinate of the outer edge of the upper-left pixel | -4518421 projected meters |
uly – y-axis map coordinate of outer edge of the upper-left pixel | +4518421 projected meters |
Temporal Information
Coverage
The temporal coverage for this data set is January 1984 through December 2019. For more recent data, see the Quicklook Arctic Weekly EASE-Grid Sea Ice Age data product.
Resolution
Weekly
Data Acquisition and Processing
Background
The method used to estimate sea ice age involves Lagrangian tracking of sea ice from week-to-week using gridded ice motion vectors (Maslanik et al. 2011; Tschudi et al. 2020). Starting in late 1978, ice age can be estimated by treating each grid cell that contains ice as a discrete, independent Lagrangian parcel and tracking the parcels at weekly time steps as they are advected by the weekly ice motions. The process can be viewed as a set of stacked planes overlying the grid used, with each plane corresponding to an age category. Parcels move around on their respective planes, independent of parcels of other age categories, which in turn lie in their own planes. To produce maps of ice age, the set of parcels for each weekly time increment is rasterized by assigning parcels to the 12.5 km x 12.5 km grid cell within which each parcel's position lies. In cases where parcels of different ages fall within a single grid cell, the age of the grid cell is assigned to the oldest parcel (Maslanik et al. 2011; Tschudi et al. 2020). Physically, this approach assumes that younger ice deforms more easily than older ice, and as such older ice will cover a greater fraction of the area within the grid cell. For example, if two parcels, one that represents first-year ice and one that represents third-year ice, both fall within the domain of a single grid cell, then the age of that cell will be assigned as third-year ice.
If the ice concentration of a grid cell remains at or above 15 percent throughout the melt season, then that parcel is assumed to have survived the summer minimum sea ice extent (typically reached in September), and the parcel's age is incremented by one year. The age of the ice is categorized as first-year ice (0-1 years old), second-year ice (1-2 years old), and so forth based on how many summer melt seasons the ice parcel survives (Tschudi et al. 2010). Note that grid cells with less than 15 percent sea ice concentration are treated as open water, even though the cells could still contain some ice.
Acquisition
The input ice motion vectors used to create this sea ice age data set are the weekly Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, Version 4. For details on how these ice motion vectors are created, see the Data Acquisition and Processing section of the sea ice motion vectors documentation.
Processing
- Input ice motion data - weekly fields from the Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, Version 4 data set - are bilinearly interpolated to a 12.5 km x 12.5 km EASE-Grid.
- Ice parcel position is computed weekly.
- Each year's ice is tracked from year to year as a Lagrangian tracer parcel that starts at the center of each grid cell and moves according to the weekly mean ice velocity.
- Ice age is discretized in yearly increments, where a year defined as the melt season which runs from one season's minimum Arctic ice extent (usually in September) to the next year's minimum.
- If a parcel remains at 15 percent or more for a melt season, then it is aged one year. If a parcel travels to a grid cell that has less than 15 percent ice concentration, the tracer parcel is assumed to have melted away.
- The age of a grid cell is the age of the oldest tracer parcel that exists in the grid cell.
Quality, Errors, and Limitations
Quality Assessment
A 15% sea ice concentration threshold was chosen to provide the most conservative possible estimates of change in areas where multiyear ice is present. For example, at the end of summer melt, a grid cell within the marginal ice zone might have a total passive microwave-derived concentration of 15 percent. Even though, upon freeze-up, 85 percent of the grid cell would consist of first-year ice, the age of that grid cell is assigned to the oldest ice that survived within that grid cell. Hence, the maps indicate the coverage of areas that contain at least some (15 percent or more) multiyear ice but do not provide information on proportions of ice of different ages within individual grid cells. The 15 percent threshold is also the standard used by other sea ice index products at NSDIC (e.g. ASINA).
Error Sources and Limitations
When age classes are aggregated into first-year and multiyear ice categories, the information is comparable to the passive and active microwave satellite-derived time series of first-year and multiyear ice analyzed by previous studies. Overall, this remote sensing-based age product is similar in nature and information content to the buoy-derived age fields produced by Rigor and Wallace (2004), but with greater spatial detail. The age estimates are restricted to open ocean areas only, where ice motion can be resolved in the microwave data. Note that this excludes the passages in the Canadian Archipelago. The cited values for ice coverage are therefore less than the actual amount of ice present in the Arctic.
Errors in the method of estimating sea ice age depend on the following ice motion errors:
- Resolution of the satellite sensor
- Geolocation and binning errors of each image pixel
- Atmospheric effects and temporal variability of the surface, especially during the summer months
The sea ice age shown in this dataset is the oldest age within each grid cell and does not necessarily indicate that all ice in that cell is of that age. Ice may also be present in grid cells that are designated as open water if the concentration is less than 15 percent.
Version History
Version
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Date Implemented
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Description
|
---|---|---|
Version 4
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March 2019
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The input ice motion data used for this data set is now derived from Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors Version 4 and extends through December 2018. Data files are now provided in netCDF format.
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Version 3
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April 2016
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The input ice motion data used for this data set is now derived from NSIDC-0116 Version 3 data.
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Version 2
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December 2014
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Initial release of these data as an NSIDC data set.
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Related Data Sets
Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors
Quicklook Arctic Weekly EASE-Grid Sea Ice Age
Contacts and Acknowledgments
Mark Tschudi
University of Colorado Boulder
Colorado Center for Astrodynamics Research
Boulder, CO 80309
Walter N. Meier
University of Colorado Boulder
449 UCB
Boulder, CO 80309-0449
J. Scott Stewart
University of Colorado Boulder
Boulder, CO 80309-0449
Chuck Fowler
University of Colorado Boulder
Boulder, CO 80309
Jim Maslanik
University of Colorado Boulder
Boulder, CO 80309
References
Cavalieri, D. J., P. Gloersen, and W. J. Campbell. 1984. Determination of Sea Ice Parameters with the NIMBUS-7 SMMR. Journal of Geophysical Research 89(D4):5355-5369. doi: 10.1029/JD089iD04p05355.
Fowler, C., W. J. Emery, and J. Maslanik. 2004. Satellite-derived evolution of Arctic sea ice Age: October 1978 to March 2003. Geoscience and Remote Sensing Letters, IEEE, 1(2), 71-74. doi: 10.1109/LGRS.2004.824741.
Maslanik, J. A., C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi and W. Emery. 2007. A younger, thinner Arctic ice cover: Increased potential for rapid, extensive sea-ice loss. Geophys. Res. Lett., 34(L24501). doi: 10.1029/2007GL032043.
Maslanik, J., J. Stroeve, C. Fowler, and W. Emery. 2011. Distribution and trends in Arctic sea ice age through spring 2011. Geophys. Res. Lett., 38(L13502). doi: 10.1029/2011GL047735.
Rigor, I.G., and J.M. Wallace, 2004. Variations in the age of Arctic sea-ice and summer sea-ice extent. Geophysical Research Letters 31: L09401. doi: 10.1029/2004GL019492.
Tschudi, M. A., Fowler, C, Maslanik, J. A., Stroeve, J. 2010. Tracking the movement and changing surface characteristics of Arctic sea ice. IEEE J. Selected Topics in Earth Obs. and Rem. Sens., 3(4). doi: 10.1109/JSTARS.2010.2048305.
Tschudi, M.A., W.N. Meier, and J.S. Stewart, 2020. An enhancement to sea ice motion and age products at the National Snow and Ice Data Center (NSIDC). The Cryosphere, 14,1519-1536. https://doi.org/10.5194/tc-14-1519-2020