Extending the U.S. National Ice Center

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Extending the U.S. National Ice Centers Sea Ice
Climatology

• Florence Fetterer1, Charles Fowler2,
• Todd Arbetter3, Walter Meier1 , Towanda Street4

1. U.S. National Snow and Ice Data Center/WDC for
   Glaciology, Boulder
2. Colorado Center for Astrodynamics Research
3. British Antarctic Survey
4. U.S. National Ice Center

MARCDAT-II, 17-20 October 2005, Exeter, UK
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NICs Sea Ice Climatology

• U. S. National Ice Center (NICs) operational
  analyses
• Mission and history
• NIC is operated by the United States Navy, the
  National Oceanic and Atmospheric Administration
  (NOAA), and the United States Coast Guard to
  provide ice services tailored to meet the
  operational requirements of U.S. national
  interests.
• NIC has produced weekly (1972-2001) or biweekly
  (2002-present) analyses of both the Arctic and
  Antarctic Ocean
• Over 1996-1997, NIC transitioned to an all
  digital chart production environment, and digital
  product output. Todays charts can be obtained as
  image files, or as GIS-compatible vector format
  files
• The EWG Sea Ice Atlas project
• In 2000, NIC released all 1972-1994 Arctic ice
  analyses in digital format as part of the
  U.S./Russia Environmental Working Group Sea Ice
  Atlas on CD-ROM.
• The EWG Sea Ice Atlas included climatological
  products
• Monthly Means, Median, Occurrence
• 5-Year Monthly Meidan, Min, Max, 1st/3rd
  Quartile, Occurrence

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NICs Sea Ice Climatology

• NIC Sea Ice Climatology Project Objective
• Update NICs climatological products (probability
  of occurrence, median ice extent, minimum ice
  extent, maximum ice extent) to cover the period
  1972-2004, based on the digital chart series.
• Further work on a researchers version of the
  NIC chart series, needed for A New Look at the
  Northern Hemisphere Sea Ice Concentration,
  NSF-funded study (H. Stern, PI) to use chart data
  for analysis of trends and variability.
• Relevance to MARCDAT
• Operational charts as a rule are more ACCURATE
  and PRECISE for ice edge position than are
  passive microwave based ice edge products
• Operational charts are the basis for the bias
  correction applied to passive microwave data to
  achieve sea ice concentration homogeneity in the
  Hadley Centre sea ice and sea surface temperature
  data set (HadISST1).

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NICs Sea Ice Climatology

• Passive Microwave compared with Ice Chart Data

Passive microwave ice concentrations are biased
low relative to observations made using other
data sources by about 10 to 20, with the bias
being greater in summer (Partington et al.,
2003). Comparisons with NIC charts reveal that
passive microwave data may not detect ice
concentrations as high as 60.
The ice edge was in about the same position in
Sept 2002 and Sept 2003, but 2003 had a wider
band of lower concentration ice within the edge
for much of the Arctic. SSM/I data put the ice
edge more often along the 60 contour line in
2003.
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NICs Sea Ice Climatology

• Data Sources
• EWG atlas EASE-Grid files
• EWG atlas GIS-type files
• Post-1994 E00 files from NIC
• Todays SIGRID-3 shape files
• Sources of inconsistencies in the 1972-present
  digital chart record
• Different source data going into analyses
• Different analysts doing the work
• For the EWG (1972-1994) conversion
• Paper to SIGRID alpha numeric coding
• SIGRID to ArcInfo
• Arc vector format to EASE-Grid
• Transition from analysis on paper to analysis on
  machines in about 1997
• Transition from 25 km to 12.5 km grid in 1997
• Inconsistencies in land masks

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NICs Sea Ice Climatology
1976
1993
Example from Partington et al showing change in
chart detail , 1976 to 1993 Over time Increase
in quality, quantity, and effective resolution of
charts
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NICs Sea Ice Climatology

• SIGRID and the Egg Code
• Operational charts coded with egg code
• Code covers concentration, stage of development,
  and form
• Egg code converted to SIGRID string
• SIGRID string identifies (is attribute of) ice
  areas (polygons) in vector format charts

See http//nsidc.org/noaa/gdsidb/
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NICs Sea Ice Climatology

• Processing
• 1972-1994 Used the Total Ice Concentration
  images provided on the Ice Atlas
• 1995-2004 Used e00 GIS files from NIC
• Converted e00 data to vector files with EASE grid
  coordinates
• Created total ice concentration images to use in
  extending the Ice Atlas climatologies
• Created partial concentration images
• Problems
• Initial problem was decoding the e00 files
  without using GIS software
• 3-4 ice charts from NIC had inconsistencies which
  were fixed by NIC
• The land mask used on the Ice Atlas differed from
  the post-1995 land mask. Solution was to combine
  them.
• Quality assessment
• Checks in code
• Visual checks (frame-by-frame and in sequence)

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NICs Sea Ice Climatology

• Created
• weekly (biweekly) images of total ice
  concentration through 2004
• 5-year, 10-year, 33-year monthly climatologies
  showing
• Median concentration
• Minimum and Maximum concentrations
• Percent Occurrence
• Partial Concentrations

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NICs Sea Ice Climatology

• Example Weekly Total Concentration

17 Sept 1974
13 Sept 2004
11 Sept 1984
14 Sept 1994
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NICs Sea Ice Climatology
Example 33-year statistics, September
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NICs Sea Ice Climatology
Example Partial Concentrations
Total Ice
Multi-Year Ice
First-Year Ice
Thin Ice
Fast Ice
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NICs Sea Ice Climatology
in 1996/1997 , NIC - Transitioned to digital
imagery (OLS/AVHRR) and digital analysis in GIS
format Started using SAR data in tactically
significant areas Now, NIC uses Quicksat to
compensate for deficiencies in SSM/I
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Conclusions/Future Work

• In collaboration with the U.S. National Ice
  Center, NSIDC has extended the EWG sea ice atlas
  to cover 1972-2004
• The combination of Ice Charts and Passive
  Microwave Data provides a more complete picture
  of the evolving Arctic sea ice cover covering
  parts of 4 decades
• The extension of sea ice observations into the
  pre-satellite era underscores the significance of
  the declining trend in sea ice cover in the 90s
  and 00s.

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References

• Arctic Climatology Project. 2000. Environmental
  Working Group joint U.S.-Russian sea ice atlas.
  Edited by F. Tanis and V. Smolyanitsky. Ann
  Arbor, MI Environmental Research Institute of
  Michigan in association with the National Snow
  and Ice Data Center. CD-ROM
• Agnew, T., and S. Howell (2003), The use of
  operational ice charts for evaluating passive
  microwave ice concentration data,
  Atmosphere-Ocean, 41, 317-331.
• Brodzik, M.J. 1996. Summary of NOAA/NASA Polar
  Pathfinder Grid Relationships. Special Report to
  the National Snow and Ice Data Center, Boulder,
  CO.
• McKenna, P., and W. N. Meier (2002), SSM/I sea
  ice algorithm inter-comparison Operational case
  studies from the National Ice Center, IGARSS
  Proceedings, Toronto, 24-28 June 2002.
• Partington, K., T. Flynn, D. Lamb, C. Bertoia,
  and K. Dedrick (2003), Late twentieth century
  Northern Hemisphere sea-ice record from U.S.
  National Ice Center ice charts, J. Geophys. Res.,
  108, 3343, doi3310.1029/2002JC001623.