Metadata for daily basin average ice concentration ====================================================== File name: daily1898-2002.txt Period: 105 winters starting 1898 and ending 2002 Records each winter: 182, staring Dec 1 and ending: 1. May 30 for leap years 2. May 31 for non-leap years Total number of Records 19110 Record Format: (i3,1x,i4,2i3,4(1x,f5.1)) field 1 = day of season (1-182) field 2 = year field 3 = month field 4 = day field 5 = lake-average ice concentration field 6 = west basin average ice concentration field 7 = center basin average ice concentration field 8 = east basin average ice concentration Units of measurement Daily basin averaged ice concentration for a given winter expressed as a percent of the surface area covered by ice. Ice cover numeric codes 1. 0.0 through 100.0 = percent of lake or basin covered by ice 2. -1.0 = missing data Distribution of modeled, observed, and average of observed data: 1. Modeled data for winters 1898-1972 (Assel 1990). 2. Observed data for winters 1973-1988 calculated based on CIS data. 3. Observed data for winters 1996-2002 calculated based on NIC data. 4. An average of CIS and NIC data, based on daily data, for winters 1989-1995. --------------------------------------------------------------------------- If the user wants the original cis and nice files for winters 1989-1995 they are available as well in cis-8995.txt and nic-8995.txt. Documentation is as given above for file structure and record format. ---------------------------------------------------------------------- Note on Modeled daily ice cover data ---------------------------------------------------------------------- A total of 75 winters (1898-1972) are based on modeled ice cover data abstracted from Assel (1990). That paper describes lake averaged ice cover trends, extremes, long-term means, and the relationship between extreme ice cover and atmospheric circulation. A second paper based on that same model (Assel 1991) documents the potential Lake Erie ice cover under greenhouse warming scenarios for each of the three Lake Erie basins. --------------------------------------------------------------------------- Note on Observed ice cover data. --------------------------------------------------------------------------- Daily ice data was calculated by linear interpolation between observed ice charts. The daily data input files are ascii grids from Assel (2003). A mask (erimasI2.txt) file was used to identify each of the Lake Erie sub-basins. A fortran program, ave.for, was used to calculate the spatial averages. There are 3577 over water grid cells for Lake Erie of which: 1. 708 grids cells compose the west basin, 2. 2039 grid cells compose the center basin, and 3. 830 grid cells compose the east basin. The spatial average for Lake Erie was calculated as a spatial weighted average of the three basin average ice cover concentrations. -------------------------------------------- Graphics of Basin Averaged Ice Concentration -------------------------------------------- Curves of basin spatial averaged ice concentration of the west basin, the center basin, and east basin were plotted on a single graph for each winter. There are 105 graphs (file names: 1898.gif....2002.gif). The graphics for 1898-1972 are for the modeled data, the graphs for 1973-1988 are for the CIS data, the graphics for 1989-1995 are for the average of the CIS and NIC data, and the graphics for 1996-2002 are for NIC data. Assel, R.A., 1990. An ice-cover climatology for Lake Erie and Lake Superior for the winter seasons 1897-98 to 1982-83, International Journal of Climatology, 10:731-748. Assel, R.A., 1991. Implications of CO2 global warming on Great Lakes ice cover. Climate Change, 18:377-395 Assel, R.A., 2003. NOAA Atlas, An Electronic Atlas of Great Lakes Ice Cover winters 1972-2003. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan 48105. Data Set Created December 2003 ------------------------------ Raymond Assel NOAA/GLERL 4840 S. State Rd. Ann Arbor, MI email: Ray.Assel@noaa.gov