Data Description
Parameters
The parameters for this data set are described in Table 1.
Table 1. Parameter Descriptions
Parameter name as it appears in the netCDF file |
Description |
Units |
---|
AHRA MO |
Earliest melt onset date derived from Advanced Horizontal Range Algorithm (AHRA) algorithm (Anderson et al. 2014) |
Day of year |
EMO |
Early melt onset date (Markus et al. 2009) |
Day of year |
EFO |
Early freeze onset date (Markus et al. 2009) |
Day of year |
CMO |
Continuous melt onset date (Markus et al. 2009) |
Day of year |
CFO |
Continuous freeze onset date (Markus et al. 2009) |
Day of year |
DOO |
Day of opening; last day the sea ice concentration drops below 80% |
Day of year |
DOR |
Day of retreat; last day sea ice concentration drops below 15% |
Day of year |
DOA |
First day of advance; first day sea ice concentration increases above 15% |
Day of year |
DOC |
First day of closing; first day sea ice concentration increases above 80% |
Day of year |
OIFP |
Outer ice-free period; DOC - DOO |
Days |
IIFP |
Inner ice-free period or the open-water period; DOA - DOR |
Days |
SLIP |
Seasonal loss of ice period; DOR - DOO |
Days |
SGIP |
Seasonal gain of ice period; DOC-DOA |
Days |
SIZ |
Seasonal ice zone |
Days |
File Information
Format
The data are provided in a single netCDF (.nc) file.
An Extensible Markup Language (.xml) file with associated metadata is also provided.
Naming Convention
The file name is:
arctic_seaice_climate_indicators_nh_v01r01_1979-2017.nc
File Size
The data file is approximately 38 MB.
Spatial Information
Coverage
Northernmost Latitude: 90° N
Southernmost Latitude: 30° N
Easternmost Longitude: 180° W
Westernmost Longitude: 180° W
Resolution
25 km
Geolocation
The following tables provide a description of the projection and grid used for this data set.
Table 2. Geolocation Details
Geographic coordinate system |
Unspecified datum based upon the Hughes 1980 ellipsoid |
---|
Projected coordinate system |
NSIDC Sea Ice Polar Stereographic North |
---|
Longitude of true origin |
-45 |
---|
Latitude of true origin |
70 |
---|
Scale factor at longitude of true origin |
1 |
---|
Datum |
Not_specified_based_on_Hughes_1980_ellipsoid |
---|
Ellipsoid/spheroid |
Hughes 1980 |
---|
Units |
meter |
---|
False easting |
0 |
---|
False northing |
0 |
---|
EPSG code |
3411 |
---|
PROJ4 string |
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs |
---|
Reference |
https://epsg.io/3411 |
---|
Table 3. Grid Details
Grid cell size (x, y pixel dimensions) |
Grid cell size varies with location |
---|
Number of rows |
448 |
---|
Number of columns |
304 |
---|
Geolocated lower left point in grid |
33.92° N, 279.26° W |
---|
Nominal gridded resolution |
25 km x 25 km |
---|
Grid rotation |
N/A |
---|
ulxmap – x-axis map coordinate of the center of the upper-left pixel (XLLCORNER for ASCII data) |
-3850 projected km |
---|
ulymap – y-axis map coordinate of the center of the upper-left pixel (YLLCORNER for ASCII data) |
5850 projected km |
---|
Temporal Information
Coverage
01 March 1979 through 28 February 2018
Resolution
Yearly
Annual sea ice paramters are tracked through February of the following year. For example, 2016 fields were derived from input sources spanning 1 March 2016 through 28 February 2017.
Data Acquisition and Processing
Background
This product contains a suite of sea ice melt-season indicators. Parameters track the evolution of the Sea Ice Concentration (SIC) from early to continuous surface melt onset, including when the ice cover opens (SIC drops below 80%); retreats, i.e. becomes open water (SIC drops below 15%); advances, i.e. ice starts to form (SIC rises above 15%); and closes (SIC increases above 80%). These sea ice descriptions provide an assessment of how the melt season is changing across the Arctic. The gridded format of these data allow these changes to be observed on a regional scale.
The melt-onset parameters are derived from Brightness Temperature (Tb) data collected on different Passive Microwave (PM) channels. Melt onset is detectable because PM Tb are sensitive to the state of water (frozen vs. liquid).
Acquisition
The data derive from Scanning Multichannel Microwave Radiometer (SMMR), Special Sensor Microwave/Imager (SSM/I), and Special Sensor Microwave Imager/Sounder (SSMIS) Brightness Temperature (Tb) observations. Input data come from the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 3 (Meier et al. 2017) and the DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures, Version 4 (Maslanik and Stroeve 2004) data sets at NSIDC.
Processing
A SIC mask is used to constrain where melt onset is calculated from Tb. This mask is derived from the Merged Goddard
parameter in the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration data set. For each grid cell and each melt-season parameter, a multi-day smoothing is applied to remove noise from synoptic events (e.g. short-term ice growth/melt or advection). Further details on processing steps, and the product in general, can be found in Biiss et al. (2019) and Peng et al. (2018).
Quality, Errors, and Limitations
First, though the data are gridded at a resolution of 25 km, the SMMR, SSM/I, and SSMIS sensors have much coarser spatial resolutions (up to ~45 km x ~70 km), so Tb observations may not capture smaller openings in the ice. Second, surface melt during the summer, and new ice formation during the fall and winter, can bias SIC estimates dervied. Surface melt tends to skew the Day of Opening (DOO) (and possibly the Day of Retreat, DOR) earlier in the year and the First Day of Advance (DOA) and the First Day of Closing (DOC) later.
Instrumentation
For a description of the SMMR, SMMI, SSMI/S instruments, visit the SMMR, SSM/I, and SSMIS Sensors Summary.
Related Data Sets
NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 3
DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures, Version 4
Version History
Table 4. Version History Summary
Version |
Summary |
---|
1.1 |
Changes and updates to this version include:
- The data record was updated through 2017.
- The full data record was also reprocessed to correct an error in the CFO field. In the previous version, the CFO field was written with a copy of the EFO field.
- Some geophysical data fields (e.g. year) were updated in the netCDF file to better reflect common netCDF practices (e.g. the year field is now labeled as time).
|
1.0 |
Initial release |
Contacts and Acknowledgments
Contacts
Michael Steele
Polar Science Center
Applied Physics Laboratory
University of Washington
Seattle, Washington 98105
Walter N. Meier
The National Snow and Ice Data Center
University of Colorado
Boulder, Colorado 80309
Angela Bliss
Earth System Science Interdisciplinary Center
University of Maryland / NASA Goddard
Baltimore, Maryland
Peng Ge
North Carolina Institute for Climate Studies, North Carrolina State University
NOAA Centers for Environmental Information (NCEI)
Raleigh, North Carolina
Acknowledgements
The data set was produced with funding from the NASA Climate Indicators program (NNH14ZDA001N-INCA).
References
Anderson, M., A. C. Bliss, and S. Drobot. 2019. Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures, Version 4. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: 10.5067/A9YK15H5EBHK
Bliss, A.C., M. Steele, G. Peng, W.N. Meier, and S. Dickinson. 2019. "Regional variability of Arctic sea ice seasonal change climate indicators from a passive microwave climate data record." Env. Res. Lett., 14, Art. No. 045003. doi: 10.1088/1748-9326/aafb84
Markus, T., J. C. Stroeve, and J. Miller. 2009. "Recent changes in Arctic sea ice melt onset, freezeup, and melt season length." J. Geophys. Res. 114(C12):C12024. doi: 10.1029/2009JC005436
Maslanik, J. and J. Stroeve. 2004. DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures, Version 4. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: 10.5067/AN9AI8EO7PX0
Meier, W. N., F. Fetterer, M. Savoie, S. Mallory, R. Duerr, and J. Stroeve. 2017. NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 3. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: 10.7265/N59P2ZTG
Peng, G., M. Steele, A.C. Bliss, W.N. Meier, and S. Dickinson. 2018. "Temporal means and variability of Arctic sea ice melt and freeze season climate indicators using a satellite climate data record." Rem. Sens., 10, Art. No. 1328. doi: 10.3390/rs10091328