Submission deadline: Monday December 8th, 2025
The Sea Ice Prediction Network South (SIPN South) is pleased to invite contributors to participate in the ninth coordinated sea-ice prediction experiment in the Southern Ocean.
Over the past eight years, we have received more than 4000 forecasts from 29 unique contributors (institutions or individuals) across five continents. We warmly thank all contributors for their interests, efforts and feedbacks. An evaluation of the forecasts collected since 2017 is available in Massonnet et al. (2023). All SIPN South contributors are automatically invited as co-authors on future papers.
Here, we outline the protocol for contributing to the summer 2025-2026 experiment. The protocol is the same as last year. All groups are invited to participate regardless of the approach they follow.
If the above schedule is too tight but a delayed contribution would still be possible, please do not hesitate to let us know and we will find a flexible solution that accommodates everyone.
Participants are invited to issue from one to five of the following diagnostics, ordered by descending priority. The submission process is described at the end of this page. The diagnostics are:
1. High priority
Diagnostic: Antarctic (circumpolar) daily mean sea-ice area from December 1st 2025 to February 28th 2026 included (90 days).
Format: One text file with one row and 90 comma-separated values, each expressing daily sea-ice area for the 31 + 31 + 28 days of the December–February period. Units must be 10⁶ km². Numbers must be rounded to four decimal digits, and trailing zeroes must be included.
File name: <<group-name>_<forecast-id>_20251201-20260228_total-area.txt where <group-name> is the name of the participating group (university, research center, institution) and <forecast-id> is a 3-digit identifier for the forecast (001, 002, …).
Remarks: ensemble forecasts are welcome. Please keep one file per forecast and increment each time the <forecast-id> by one unit: 001 for the first forecast, 002 for the second, etc. If only one forecast is submitted, set <forecast-id> to 001.
2. Medium priority
Diagnostic: February Antarctic daily mean sea-ice area per 10° longitude bin, from December 1st 2025 to February 28th 2026 included (90 days).
Format: One text file with 36 rows each displaying 90 comma-separated values following the same requirements as diagnostic 1.
Each row corresponds to a 10° longitude bin:
First row: 0° ≤ longitude < 10°
Second row: 10° ≤ longitude < 20° … 36th row: 350° ≤ longitude < 360°
File name: <group-name>_<forecast-id>_20251201-20260228_regional-area.txt
Remarks: Same rules for ensemble forecast indexing as in diagnostic 1.
3. Low priority
Diagnostic: February Antarctic daily mean sea-ice concentration
Format: A NetCDF file with 90 timesteps (one per day from December 1st 2025 to February 28th 2026). Each timestep displays the spatial field of sea-ice concentration. The file format must follow CMIP6 conventions:
longitude and latitude.sftof (percentage of the grid cell covered by ocean, units %).areacello (units m²).File name: <group-name>_<forecast-id>_20251201-20260228_concentration.nc
Remarks: Same rules for ensemble forecast indexing as in diagnostic 1.
4. Low priority
Diagnostic: February Antarctic daily mean grid cell thickness (or equivalently: mean sea-ice volume per unit grid cell area, or actual sea-ice thickness × sea-ice concentration)
Format: A NetCDF file with 90 timesteps (one per day from December 1st 2025 to February 28th 2026). Each timestep displays the spatial field of mean grid cell thickness. The file format must follow CMIP6 conventions:
sivol and has units of meters.longitude and latitude.sftof (percentage of the grid cell covered by ocean, units %).areacello (units m²).File name: <group-name>_<forecast-id>_20251201-20251228_volume.nc
Remarks: Same rules for ensemble forecast indexing as in diagnostic 1.
5. Low priority (long forecasts)
Diagnostic: Antarctic (circumpolar) monthly mean sea-ice area from forecasts initialized in 2025 (any date) and extended at least 6 months into 2026.
Format: One text file with one row and comma-separated monthly values. Units must be 10⁶ km². Numbers must be rounded to four decimal digits with trailing zeroes.
File name: <group-name>_<forecast-id>_2025mm-2026MM_total-area-long-forecast.txt where <group-name> is the name of the participating group, <forecast-id> is a 3-digit identifier (001, 002, …), mm and MM are the first and last months of the forecasts, respectively.
Remarks: Same rules for ensemble forecast indexing as in diagnostic 1.
The forecasts will be assessed against two observational references:
The submission of a forecast by a group is done in two steps.
The deadline for submitting the online form (containing the link pointing towards the data) is the Monday December 8th, 2025
All forecast and verification data will be made publicly available, as for the previous exercises. The SIPN South Github repository hosts all data collected up to now from the project.
Please send an e-mail directly to François Massonnet to be added to the mailing list.