Integrated Climate Data Center
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Antarctic polynyas

CliSAP/KlimaCampus Product

Sample maps of the polynya / thin ice distribution around Antarctica for July 31 2000 (left) and August 2 2007 (right). Polynya areas are denoted blue (predominantly open water) and dark cyan (thin ice, < 10-20 cm). The data set focusses on coastal polynyas; areas far off the coast are flagged.

 

Access

UNRESTRICTED

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RESTRICTED only accessable in ZMAW net or via CliSAP login  What does that mean?

Data access via file system: /data/icdc/ice_and_snow/ssmi_polynya

 

Description

Data of the Special Sensor Microwave / Imager (SSM/I) were used to identify and map polynyas; these are areas of open water and/or thin (< 20 cm) sea ice in regions of typically thick sea ice.

For this purpose a classification method was applied to gridded 37 GHz and 85 GHz SSM/I brightness temperature measurements of each SSM/I overpass to distinguish between three surface types: thick ice, thin ice, and open water.

Polynya maps were obtained for each SSM/I overpass (inter-sensor difference corrected data of DMSP-platforms f10, f13 and f15), quality controlled and merged to maps showing the daily winter-time polynya distribution.

The offered data set (version 01) contains a mean daily composite of the polynya distribution as well as an estimate of the minimum polynya distribution - as a conservative estimate of a likely lower bound of the polynya area.

The basic algorithm is described in Markus and Burns (1995) and Hunewinkel et al. (1998). The modifications that were required to obtain a circum-Antarctic polynya distribution and further details can be found in Kern et al. (2007) and the project report.

 

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Parameters

Number of satellite overpasses 1/day  
Name Unit Values
Mean polynya distribution none 0: open water
    30: thin ice (< 10-20 cm)
    90 & 100: thick ice
    180: land
    220: missing & flagged data
Minimum polynya distribution none see above

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Coverage, spatial and temporal resolution

Period and temporal resolution:

  • 1992-2008, May to September, respectively
  • Daily

Coverage and spatial resolution:

  • Southern hemisphere (without northern part of Antarctic Peninsula and the region between 130°W and 155°W)
  • Spatial resolution: 5 km x 5 km; polar-stereographic grid, tangential plane at 70°S
  • Geographic Longitude: -180°E to 180°E
  • Geographic Latitude: about 40°S to 90°S
  • Dimension: 1520 columns x 1660 rows
  • Altitude: 0.0 m

Format:

  • netCDF

Upon request we offer data of the polynya distribution for every subregion used, e.g. the Ross Sea, also as a daily composite or for every SSM/I overpass (depending on the region up to 6/day) for the same time period on the same grid with the same grid resolution also in netCDF format.

 

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Data quality

The data set does not contain uncertainty estimates*.

According to Markus and Burns (1995) changes in polynya area as small as 50 km² can be identified with a mean accuracy of the obtained polynya area of 80 km². We suggest a more conservative estimate of both numbers of 200 km². Error contributions come from (see also: Publications)

  • inaccurate / too old coastline**
  • dynamically changing shelf ice borders**
  • influence of fast ice, shelf ice, and ice bergs on the classification
  • weather influence
  • Smearing of strong contrasts due to coarse spatial resolution

*) The daily polynya distribution data available upon request for the single sub-regions contain besides the mean daily composite polynya distribution also an estimate of the maximum and the minimum polynya distribution.

**) In order to mitigate this influence, a new landmask with 5 km grid resolution was created from clear-sky NOAA-AVHRR imagery. This landmask is included in the data set. It is kind of a dynamic coastline as it has been updated every two years for 1992-2004.

 

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Contact

Stefan Kern

CliSAP / KlimaCampus / ICDC

Email: stefan.kern@zmaw.de

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Data citation

When using this data please cite like follows:

Kern, S. (2012) Antarctic daily winter-time polynya distribution from SSM/I brightness temperature data, http://icdc.zmaw.de/polynya_ant.html , (years used), Integrated Climate Data Center (ICDC), CEN, University of Hamburg, Hamburg, Germany, Digital Media.

PLUS the paper Kern et al., 2007 from the References.

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