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Quicklook Arctic Weekly EASE-Grid Sea Ice Age, Version 1
This data set is the quicklook version of the EASE-Grid Sea Ice Age product (https://nsidc.org/data/nsidc-0611). It is derived from the Quicklook Arctic Weekly EASE-Grid Sea Ice Motion Vectors data set (https://nsidc.org/data/nsidc-0748).
This is the most recent version of these data.
Initial Release
STANDARD Level of Service
Data: Data integrity and usability verified
Documentation: Key metadata and user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools
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Geographic Coverage |
- If you are not currently logged in to Earthdata, you will be prompted to do so.
- You may register for an Earthdata Login if you do not have an account.
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, and J. S. Stewart. 2019. Quicklook Arctic Weekly EASE-Grid Sea Ice Age, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/2XXGZY3DUGNQ. [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
The netCDF file contains one value of sea ice age for each week, 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.
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Value
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Description
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|---|---|
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0
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Open water or < 15% sea ice concentration
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1, 2, 3, ..., 16
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Sea ice age; higher age estimates are not precise, so older ices, 5th-year (4-5 years old) and above, are generally considered together
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20
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Designates the grid cells that contain only land
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21
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Designates grid cells that contain ocean for which ice age was not calculated
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Sample Browse Image
One browse image displaying sea ice age is provided for every week of data. Figure 1 shows a sample browse image.
Figure 1. Sample browse image displaying sea ice age for the week of 01 January through 07 January 2019.
File Naming Convention
The data files are named according to the following convention and as described in Table 2:iceage_hh_rrrr_<start-date>_<end-date>_ql.ext
Example:iceage_nh_12.5km_20190101_20190415_ql.nc
iceage_nh_12.5km_20000101_20000107_ql.png
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Variable
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Description
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|---|---|
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hh
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Hemisphere (nh = Northern)
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rrrr
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Resolution of input data source in km (e.g. 12.5 km)
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<start-date>
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First day of data contained in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format
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<end-date>
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Last day of data contained in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format
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ql
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Indicates this file is part of the Quicklook Arctic Weekly EASE-Grid Sea Ice Age product
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| ext | Extension; .nc for netCDF file or .png for browse images |
File Size
The netCDF file size varies from approximately 0.5 to 3.5 MB, depending on how many weeks of data are included in the file.
Browse images are approximately 400 KB.
Spatial Information
Coverage
This data set covers the Arctic Ocean within the boundaries defined below:
Southernmost Latitude: 29.7° N
Northernmost Latitude: 90.0° N
Westernmost Longitude: 180.0° W
Easternmost Longitude: 180.0° E
.png)
Resolution
12.5 km
Geolocation
Data are projected using a 12.5 km Northern Hemisphere EASE-Grid. The grid is shifted by half a grid cell relative to the standard version of EASE-Grid, which has the center of the grid right over the pole. More details can be found in the tables below. More details on EASE-Grid can be found on the EASE Grids website.
| Geographic coordinate system | Unspecified datum based upon the International 1924 Authalic Sphere |
|---|---|
| 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 | Not specified based on International 1924 Authalic Sphere |
| 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 |
| ulxmap – x-axis map coordinate of the outer edge of the upper-left pixel (XLLCORNER for ASCII data) | -4,518,421 projected meters |
| ulymap – y-axis map coordinate of the outer edge of the upper-left pixel (YLLCORNER for ASCII data) | 4,518,421 projected meters |
Temporal Information
Coverage
Data coverage varies and changes with time. This data set begins the week after the last day of data in the EASE-Grid Sea Ice Age, Version 4 product and is extended approximately monthly. When the EASE-Grid Sea Ice Age, Version 4 data set is extended, this quicklook product is updated so that the two data sets do not overlap.
Resolution
Weekly
Data Acquisition and Processing
Background
This data set is a sister product to the EASE-Grid Sea Ice Age, Version 4 data set. Users should refer to the EASE-Grid Sea Ice Age, Version 4 user guide for more information.
Acquisition
The input ice motion vectors used to create this sea ice age data set are the weekly Quicklook Arctic Weekly EASE-Grid Sea Ice Motion Vectors, Version 1 data sets.
Processing
Note: The general processing steps for this data set mirror those of the EASE-Grid Sea Ice Age, Version 4 data set and are described below.
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Input ice motion data from the Quicklook Arctic Weekly EASE-Grid Sea Ice Motion Vectors, Version 1 data set are bilinearly interpolated to a 12.5 km x 12.5 km EASE-Grid. A sea ice mask, derived from the Near-Real-Time DMSP SSMIS Daily Polar Gridded Sea Ice Concentrations, Version 1 data set, is applied.
- 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; tracer parcels may not end in the same grid cell in which they started.
- Ice parcel positions are computed weekly.
- Ice age is discretized in yearly increments. A year is 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 an ice parcel remains at 15 percent or more for a melt season, then it has aged one year. If a parcel travels to a new grid cell that has less than 15 percent ice concentration, the origianl ice 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%. Even though, upon freeze-up, 85% 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 show areas that contain at least some (15% or more) multiyear ice but do not provide information on the ratio of different ice ages within individual grid cells.
Error Sources and Limitations
When ice age is classified, the information can be compared to satellite-derived time series of ice age. Overall, this remote-sensing-based age product is similar to the buoy-derived ice ages 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 using microwave satellite data. Note, since this excludes the passages in the Canadian Archipelago, the cited values for ice coverage are less than the actual amount of ice present in the Arctic.
Errors in estimating sea ice age depend on the following factors:
- 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%.
Related Data Sets
Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors
Quicklook Arctic Weekly EASE-Grid Sea Ice Motion Vectors
MEaSUREs Arctic Sea Ice Characterization 25 km EASE-Grid 2.0
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
References
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
