NOAA/NSIDC CDR¶

NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration (G02202, Version 6) / Near-Real-Time NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration (G10016, Version 4)

Available

At a glance¶

Note on period: Daily data begin on 25 October 1978 and monthly data in November 1978. The final CDR (G02202) runs through the most recent processing, about three weeks behind real time; the Near-Real-Time CDR (G10016) fills the gap and covers roughly the last three months. A gap exists from 3 December 1987 through mid-January 1988 due to satellite issues.

Overview¶

A Climate Data Record (CDR) of sea ice concentration from passive microwave data, produced by NSIDC under the NOAA CDR Program for both polar regions since 1978. It combines concentration estimates from the NASA Team and NASA Bootstrap algorithms with a rule-based method, and provides the spread between the two as an uncertainty estimate (standard deviation). Brightness temperatures from SMMR, SSM/I and SSMIS — and, from 2025, AMSR2 — feed a consistent daily and monthly time series on the same 25 km polar stereographic grids. It is widely used for studies of Arctic and Antarctic sea ice area and extent. (The NSIDC Sea Ice Index is a separate product computed from NSIDC-0051 and NSIDC-0803, not from this CDR.)

What changes with the successor¶

NOAA/NSIDC CDR V5 → NOAA/NSIDC CDR V6¶

Transition: 2026-01

Version 6 switches the input brightness temperatures from 1 January 2025 onward to JAXA AMSR2, ahead of the loss of the ageing and increasingly unreliable DMSP SSMIS data stream. The grids and variables are essentially those of V5, except that the V5 AMSR2 prototype group has been removed and a bug in the land spillover correction has been fixed. Differences over 1978–2024 are very small, but V5 access ended in June 2026, so the full record has to be downloaded again as V6.

Sources: NSIDC announcement — New version release: NOAA/NSIDC Sea Ice Concentration Data Records - CDR Version 6 and Near-Real-Time CDR Version 4 (2026-01-15) · NSIDC Special Report 29 — NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration Version 6 Updates (Windnagel, Meier, Fetterer, 2026) · G02202 Version 6 User Guide · G02202 Version 5 User Guide · G10016 Version 4 User Guide · NOAA@NSIDC Data Updates (V5 and V3 retired 2026-06-17)

Available variables¶

Daily-file variables as listed in the Version 6 user guide. Concentrations are stored as bytes 0–100 with scale_factor 0.01, so they usually read as fractions 0–1. Supplementary variables sit in the cdr_supplementary group. Monthly files use cdr_seaice_conc_monthly, cdr_seaice_conc_monthly_stdev and cdr_seaice_conc_monthly_qa. V4's nsidc_bt_seaice_conc and nsidc_nt_seaice_conc were renamed raw_bt_seaice_conc and raw_nt_seaice_conc in V5.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Sea ice concentration (main group)¶

Quality and interpolation flags (main group)¶

Supplementary variables (cdr_supplementary group)¶

The full variable list is in the official documentation.

How to get the data¶

• NSIDC data set page — G02202 Version 6 (final CDR) — Web documentation / HTTPS directory download
  • User guide, C-ATBD, version-change report (Special Report 29) and a sign-up form for update notifications.
• NOAA@NSIDC HTTPS archive — G02202_V6 — HTTPS (browser, wget, Python/R scripts) No login needed
  • No login needed. Daily and monthly files are under north/ and south/, and yearly aggregated daily files are also available.
• NSIDC data set page — G10016 Version 4 (Near-Real-Time CDR) — Web documentation / HTTPS (https://noaadata.apps.nsidc.org/NOAA/G10016_V4/) No login needed
  • Provisional data covering about the last three months. Replace that period with G02202 once the final CDR is available.
• NOAA NCEI Sea Ice Concentration CDR page — Web documentation (documents, source code, maturity matrix)
• How to access NOAA@NSIDC data sets via PolarWatch (help article) — ERDDAP (subsetting, format conversion)
  • Check the PolarWatch dataset ID first to confirm that it serves Version 6.

Example code¶

Download over HTTPS without logging in. File names follow sic_ps25_.nc (satellite codes such as F17 or am2), so check the exact names in the directory listing.

# Mirror the Northern Hemisphere V6 daily directory (better to restrict to the year folders you need)
wget -r -np -nH --cut-dirs=3 -A "*.nc" -e robots=off \
  https://noaadata.apps.nsidc.org/NOAA/G02202_V6/north/daily/

# In Python, open the supplementary group separately
# xr.open_dataset(f)                               -> cdr_seaice_conc, etc.
# xr.open_dataset(f, group="cdr_supplementary")    -> raw_bt_seaice_conc, etc.

Practical tips¶

• The same date can have different values in the final CDR (G02202) and the Near-Real-Time CDR (G10016): the near-real-time product is provisional and lacks some quality control and temporal interpolation. Base published analyses on the final CDR, fill only the last few weeks with near-real-time data, and replace them later.
• From 1 January 2025 the input sensor is AMSR2 instead of SSMIS (F17). NSIDC adjusted AMSR2 to match SSMIS and reports differences within the data uncertainty, but it is still safest to flag the sensor change in trend or anomaly analyses that compare periods before and after 2025.
• The pole hole is filled by interpolation and flagged as 100 in surface_type_mask. Its size depends on the sensor (north of 84.1°N for SMMR, 86.7°N for SSM/I, 89.0°N for SSMIS, 88.5°N for AMSR2), which can affect late-summer and early-autumn trends and climatologies.
• The polar stereographic grid is not equal-area, so cell areas vary. When computing sea ice area yourself, do not simply multiply by 25 km × 25 km — use the latitude-dependent cell areas.

Notices and change history¶

References for your paper¶

Dataset citation¶

Final CDR — G02202 Version 6 — DOI 10.7265/b18j-z797

@misc{nsidc_g02202_v6,
  author    = {Meier, W. N. and Fetterer, F. and Windnagel, A. K. and Stewart, J. S. and Stafford, T.},
  title     = {{NOAA/NSIDC} Climate Data Record of Passive Microwave Sea Ice Concentration ({G02202}, Version 6)},
  year      = {2026},
  publisher = {National Snow and Ice Data Center},
  address   = {Boulder, Colorado USA},
  doi       = {10.7265/b18j-z797}
}

Near-Real-Time CDR — G10016 Version 4 — DOI 10.7265/tm2n-1m33

Reference papers¶

CDR methodology paper — DOI 10.5194/essd-5-311-2013

@article{peng2013cdr,
  author  = {Peng, G. and Meier, W. N. and Scott, D. J. and Savoie, M. H.},
  title   = {A long-term and reproducible passive microwave sea ice concentration data record for climate studies and monitoring},
  journal = {Earth System Science Data},
  volume  = {5},
  number  = {2},
  pages   = {311--318},
  year    = {2013},
  doi     = {10.5194/essd-5-311-2013}
}

CDR verification paper (optional) — DOI 10.3402/polar.v33.21004

AMSR2 operational sea ice concentration paper (optional, relevant to the 2025+ input) — DOI 10.1109/JSTARS.2017.2693120

Acknowledgements¶

NSIDC requires citation of the data set as a condition of use. Give the version (V6) and DOI, the period and hemisphere used, and the date accessed. If you discuss the algorithm in detail, NSIDC also recommends citing the C-ATBD (Rev. 12).

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• G02202 Version 6 User Guide
• NSIDC Special Report 29 — Version 6 Updates
• C-ATBD (Rev. 12, Sea Ice Concentration V6)
• Descriptions of and differences between the NASA Team and Bootstrap algorithms (NSIDC Help Center)
• NOAA@NSIDC Data Updates
• This site — AMSR2 ASI 6.25 km sea ice concentration