Extending the U.S. National Ice Center’s Sea Ice Climatology Florence Fetterer 1, Charles Fowler 2, Todd Arbetter 3, Walter Meier 1, Towanda Street 4 MARCDAT-II, October 2005, Exeter, UK 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

NIC’s Sea Ice Climatology U. S. National Ice Center ( NIC’s) operational analyses  Mission and history o 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. o NIC has produced weekly ( ) or biweekly (2002-present) analyses of both the Arctic and Antarctic Ocean o Over , NIC transitioned to an all digital chart production environment, and digital product output. Today’s charts can be obtained as image files, or as GIS-compatible vector format files The EWG Sea Ice Atlas project o In 2000, NIC released all Arctic ice analyses in digital format as part of the U.S./Russia Environmental Working Group Sea Ice Atlas on CD-ROM. o The EWG Sea Ice Atlas included climatological products  Monthly Means, Median, %Occurrence  5-Year Monthly Meidan, Min, Max, 1st/3rd Quartile, %Occurrence

 NIC Sea Ice Climatology Project Objective o Update NICs climatological products (probability of occurrence, median ice extent, minimum ice extent, maximum ice extent) to cover the period , based on the digital chart series. o Further work on a “researcher’s 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 o Operational charts as a rule are more ACCURATE and PRECISE for ice edge position than are passive microwave based ice edge products o 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). NIC’s Sea Ice Climatology

Passive Microwave compared with Ice Chart Data Mid-September 2002 Mid-September 2003 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.

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

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

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 NIC’s Sea Ice Climatology

Processing : Used the Total Ice Concentration images provided on the Ice Atlas : 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)

Created:  weekly (biweekly) images of total ice concentration through 2004  5-year, 10-year, 33-year monthly climatologies showing: o Median concentration o Minimum and Maximum concentrations o Percent Occurrence  Partial Concentrations NIC’s Sea Ice Climatology

Example: Weekly Total Concentration NIC’s Sea Ice Climatology 14 Sept Sept Sept Sept 1974

NIC’s Sea Ice Climatology Example: 33-year statistics, September

NIC’s Sea Ice Climatology Total IceMulti-Year IceFirst-Year Ice Thin IceFast Ice Example: Partial Concentrations

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 NIC’s Sea Ice Climatology

Conclusions/Future Work In collaboration with the U.S. National Ice Center, NSIDC has extended the EWG sea ice atlas to cover 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.

References Arctic Climatology Project 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, Brodzik, M.J 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, June 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, doi: /2002JC