Data files are formatted in Network Common Data Form, Version 4 (NetCDF-4) (.nc) following version 1.6 of the Climate and Forecast (CF) metadata conventions. For more information about working with NetCDF formatted data, visit the UCAR Unidata Network Common Data Form (NetCDF) Web site.
Documentation for MEaSUREs Northern Hemisphere State of Cryosphere Weekly 100km EASE-Grid 2.0, Version 1
Detailed Data Description
This data set utilizes three variables to represent Northern Hemisphere snow cover and sea ice extent from 2 January 1979 through 31 December 2012. These variables report:
- The location of snow cover and Arctic sea ice at 100 km resolution, generated by merging snow cover from the MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0 data set with sea ice from the MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0 data set
- Melt onset status at 100 km resolution across the Greenland Ice Sheet and Arctic sea ice, generated from the MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0 and MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0 data sets
- The level of agreement between two snow cover maps in the MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0 data set
Data are available on the HTTPS site in the https://n5eil01u.ecs.nsidc.org/MEASURES/NSIDC-0535.001/
directory. Within this there are folders labeled by year that contain all the weekly data files for that year.
This section explains the file naming convention used for this data set with an example.
Example File Name: socw100e2_19790102_19790108_v01r01.nc
socwxxxe2_YYYYMMDD_yyyymmdd_v01r01.nc
Refer to Table 1 for the valid values for the file name variables listed above.
Variable | Description |
---|---|
soc |
State of Cryosphere |
w |
Weekly |
xxx |
Resolution (km) |
e2 |
EASE-Grid 2.0 |
YYYYMMDD |
First day of week (year, month, and day) |
yyyymmdd |
Last day of week (year, month, and day) |
v01r01 |
Version 1.1 |
.nc |
netCDF-formatted file |
Data files are approximately 160 KB. The entire data set is approximately 275 MB.
Northern Hemisphere
Southernmost Latitude: 0.0°
Northernmost Latitude: 90.0°
Westernmost Longitude: -180.0°
Easternmost Longitude: 180.0°
Spatial Resolution
100 km
Projection and Grid Description
Data are provided in the 100 km Northern Hemisphere Equal Area Scalable Earth Grid 2.0 (EASE-Grid 2.0). Grid dimensions are 180 x 180. For a complete description of EASE-Grid 2.0, visit NSIDC's EASE-Grid 2.0 Format Description page.
2 January 1979 - 31 December 2012
Temporal Resolution
This data set consists of weekly snow and sea ice cover. Each week runs from Tuesday through the following Monday.
Snow cover, sea ice cover, and status of melt onset are the primary parameters in this data set. Data files also include latitude and longitude arrays that specify the center of each 100 km EASE-Grid 2.0 cell, coordinate system parameters, and the number of days since the beginning of the data record.
Variable Description
Data files contain the variables listed in Table 2.
Variable Name | Description | Dimensions | Data Type |
---|---|---|---|
merged_snow_and_sea_ice_extent |
Merged snow and sea ice cover | 180 x 180 | byte (signed) |
status_of_melt_onset |
Status of melt onset for Greenland and Arctic sea ice | 180 x 180 | byte (signed) |
snow_agreement_with_cdr |
Indicates whether MW snow cover agrees with SCE CDR¹ | 180 x 180 | byte (signed) |
latitude |
Latitude at the center of each 100 km EASE-Grid 2.0 cell | 180 x 180 | float² |
longitude |
Longitude at the center of each 100 km EASE-Grid 2.0 cell | 180 x 180 | float² |
cols |
x coordinate, center of 100 km EASE-Grid 2.0 cell (m from origin) | 1 x 180 | int |
rows |
y coordinate, center of 100 km EASE-Grid 2.0 cell (m from origin) | 180 x 1 | int |
coord_system |
EASE-Grid 2.0 grid and projection parameters | — | char |
time |
Days since 12/31/1978 | — | int |
¹Passive microwave (MW) derived snow cover; NOAA/NCDC Northern Hemisphere Snow Cover Extent Climate Data Record (SCE CDR). ²32-bit single precision floating point. Fill value for grid corners = -999. |
Parameter Range
The merged_snow_and_sea_ice_extent
, status_of_melt_onset
, and snow_agreement_with_cdr
variables, refer to Table 3 for more information, use coded integers to indicate the location of snow and sea ice, the status of melt onset on the Greenland Ice Sheet and Arctic sea ice, and whether snow cover derived from passive microwave (MW) brightness temperatures agrees with the NOAA/NCDC Northern Hemisphere Snow Cover Extent Climate Data Record (SCE CDR). The merged snow and sea ice extent variable also indicates the location of the pole hole.
The following tables contain keys to the values stored in this data set's snow and sea ice cover variables.
Value | Description |
---|---|
10 |
Snow covered land |
20 |
Snow free land |
30 |
Sea ice cover |
40 |
Open water |
90 |
Missing |
91 |
Pole hole |
-99 |
Fill value for grid corners |
Value | Description |
---|---|
0 |
No melt data |
51 |
Melt onset begins prior to file date |
52 |
Melt onset begins on file date |
53 |
Melt onset begins on a future date |
-99 |
Fill value for grid corners |
Value | Description |
---|---|
0 |
MW does not agree with SCE CDR snow cover¹ |
1 |
MW agrees with SCE CDR¹ |
90 |
No comparison |
-99 |
Fill value for grid corners |
¹Passive microwave (MW) derived snow cover; NOAA/NCDC Northern Hemisphere Snow Cover Extent Climate Data Record (SCE CDR). |
Software and Tools
Unidata at the University Corporation for Atmospheric Research maintains an extensive list of freely available Software for Manipulating or Displaying NetCDF Data.
Data Acquisition and Processing
The following sections describe how each of the variables in this data set were generated. All variables were reconciled with EASE-Grid 2.0 Land-Ocean-Coast-Ice (LOCI) masks obtained from the EASE-Grid 2.0 Land-Ocean-Coastline-Ice Masks Derived from Boston University MODIS/Terra Land Cover Data data set.
Processing Steps
Snow cover was obtained directly from the weekly_climate_data_record_snow_cover_extent
variable in the MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0 data set. Arctic sea ice extent was obtained from the sea_ice_cover variable in MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0. When these variables were reconciled with their corresponding 100 km and 25 km EASE-Grid 2.0 LOCI masks, changes to the original data were stored using separate codes. For example, the snow cover extent variable contains different values for "snow covered land" and "ocean converted to snow covered land." These values were combined for the purposes of this data set.
The merged_snow_and_sea_ice_extent
variable was generated as follows:
- Weekly sea ice maps were created from daily files by selecting Monday's value as the representative value for each cell, each week. If Monday's data was missing, Sunday's was used instead. If neither day was available, the value for that cell was filled as missing. This approach—using data weeks that run from Tuesday through the following Monday—was adopted to match the convention used by snow cover source data.
- Weekly sea ice maps were re-gridded from 25 km to 100 km using Mapx and compared with the 100 km EASE-Grid 2.0 LOCI mask. In cases where land mask mismatches converted a pixel from land to ocean, the discrepancy was reconciled by applying a 3x3 moving box filter through several passes. On the first pass, the filter examined the eight cells surrounding the converted cell and assigned it as sea ice cover if more than 50 percent contained ice. Otherwise the cell was assigned the value for open water. Subsequent iterations reassigned pixels if at least 33 percent of the surrounding cells were ice covered. Iterations were continued until no more changes were found.
- Values for ocean and land from the 100 km EASE-Grid 2.0 LOCI mask were written to an intermediate array.
- Values for snow covered land and ocean converted to snow covered land were written to the array using the coding scheme in Table 3.
- Values for sea ice were written to the array using the coding scheme in Table 3.
- Data from the intermediate array were written to the
merged_snow_and_sea_ice_extent
NetCDF variable.
For details about the snow cover source data, refer to the Data Acquisition and Processing section in MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0. For details about the Arctic sea ice cover source data, refer to the Data Acquisition and Processing section in MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0.
Processing Steps
Status of melt onset over Arctic sea ice was derived from the status_of_melt_onset
variable in MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0. Status of melt onset over Greenland was calculated at the University of Georgia using melt onset dates from MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0. These variables were reconciled with the 25 km EASE-Grid 2.0 LOCI mask when generated for their respective data sets.
Status of melt onset is created by assigning integer values which indicate whether the cell has a melt onset date prior to the current day, on the current day, or later in the year. Cells with no melt onset date are filled with 0 (see Table 5). Melt onset is only calculated for days 61-245 of the year. This range corresponds to 2 March through 2 September in non-leap years and 1 March through 1 September in leap years. Days that lie outside this range are filled with 0.
The combined Arctic-Greenland status of melt onset variable for this data set was generated as follows:
- Weekly maps were created from daily files by selecting Monday's value as the representative value for each cell, each week. If Monday's data was missing, Sunday's was used instead. If neither day was available, the value for that cell was filled as missing. This approach—using data weeks that run from Tuesday through the following Monday—was adopted to match the merged snow and sea ice cover variable described in the preceding section.
- Weekly status of melt onset maps over Arctic sea ice and Greenland were regridded to 100 km EASE-Grid 2.0 using Mapx.
- Values for status of melt onset over Arctic sea ice and Greenland were written to an intermediate array using the coding scheme in Table 4.
- The data were written to the
status_of_melt_onset
NetCDF variable.
For details about the Arctic Sea Ice and Greenland source data were derived, refer to the Data Acquisition and Processing section in MEaSUREs Arctic Sea Ice Characterization Daily 25km EASE-Grid 2.0 and MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0.
Processing Steps
The snow_agreement_with_cdr
variable was calculated from the MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0 data set, which contains both SCE CDR and MW-derived snow cover. This data set also contains the variable merged_snow_cover_extent
, which specifies for each cell whether the SCE CDR, MW-derived snow cover, or both indicate snow.
The snow_agreement_with_cdr
variable offers a different representation of snow cover in that it reports whether MW-derived snow cover agrees with the SCE CDR. snow_agreement_with_cdr
was generated from merged_snow_cover_extent
as follows:
MW agreement was calculated and written to an intermediate array using the coding scheme in Table 5.
Areas where no comparison was performed due to missing data and areas covered by permanent ice in the 100 km EASE-Grid 2.0 LOCI mask were written to the array using the coding scheme in Table 5.
Data from the intermediate array were written to the snow_agreement_with_cdr NetCDF variable.
For details about the SCE CDR, MW-derived snow cover, and merged_snow_cover_extent variable, refer to the Data Acquisition and Processing section MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Weekly 100km EASE-Grid 2.0 for more information.
Version History
Version 1.1 was released in July, 2015. Refer to Table 6 for this data set's version history.
Version | Description |
---|---|
V1.1 (Jul, 2015) |
|
V1 (Feb, 2015) | Initial version |
Error Sources
Missing data represents the biggest impact to overall data quality, as all the input products lack some daily files during the period of record.
The SCE CDR snow cover maps are not constructed according to a formal algorithm, but instead rely on the expertise of trained analysts. Furthermore, because these maps agenerated from workstation software that is continually being evaluated and improved, changes in mapping methodologies have occurred over time. Passive microwave derived snow and sea ice cover is subject to errors carrying through from the input data to the output. For details about potential errors in snow and sea ice cover derived from passive microwave brightness temperatures, refer to the Error Sources section in MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0 and MEaSUREs Arctic Sea Ice Characterization Daily 25 km EASE-Grid 2.0 for more information.
References and Related Publications
Contacts and Acknowledgments
Investigator(s) Name and Title
David A. Robinson
Rutgers University
Department of Geography
54 Joyce Kilmer Avenue
Piscataway, NJ 08854
Mark R. Anderson
University of Nebraska-Lincoln
Department of Earth and Atmospheric Sciences
214 Bessey Hall
Lincoln, NE 68588
Thomas W. Estilow
Rutgers University
Department of Geography
54 Joyce Kilmer Avenue
Piscataway, NJ 08854
Thomas L. Mote
University of Georgia
Department of Geography
210 Field Street
Athens, GA 30602
These data were generated with support from Award NNX08AP34A from the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Program.
The investigators wish to thank:
- Mary Jo Brodzik at NSIDC for technical assistance, gridding and software support, and for advice regarding the EASE Grid-2.0 format
- Donna Scott at NSIDC for technical support, documentation and metadata support, and for serving as this project's liaison
- Members of the Northern Hemisphere Snow and Ice MEaSUREs team, including Angela Bliss, Gina Henderson, and Mark Tschudi
Document Information
DOCUMENT CREATION DATE
February 2015
DOCUMENT REVISION DATE
July 2015