| Summary: | Progress Code: completed Statement: Methods Sea ice extents were calculated from passive microwave estimates of mean sea ice concentration (Cavalieri et al., 1996 updated 2008; Meier et al., 2006 updated quarterly). Seasonal maximum extent A season was considered to extend from the 1st of July of one year to 30th of June of the next. The extent of sea ice for a season was computed by searching for all pixels that were covered by at least 15% sea ice during at least one month of the season. The maximum latitude of sea ice extent was then calculated in one-degree longitude sectors, with sectors centred on integer longitudes from 179W to 180E. Areas of open water fully enclosed within the sea ice were disregarded for the purposes of calculating maximum latitude. Isolated regions of ice lying to the north of the main ice pack were also disregarded if they were separated from the main pack by at least 2 degrees of latitude (there were only a small number of instances of this situation). Daily maximum extent The maximum latitude of sea ice extent was calculated from daily estimates of sea ice concentration. Due to the increased presence of false ice in daily data (compared to monthly), an additional filtering step was applied during the calculation of daily extents. This filtering removed any areas of sea ice that were isolated from the Antarctic continent and which were less than 10 pixels in extent. The maximum latitude of sea ice was then calculated along transects centred on each integer degree of longitude. The area of open water lying to the south of the ice edge was also calculated for each transect (expressed as a fraction of the total area between the ice edge and the coastline). These data give the maximum extent of sea ice in the southern hemisphere by day and by winter season and the mean maximum extent by month. Data cover the 1979/1980 to 2007/2008 seasons. The data are available in csv files and, in the case of the mean monthly data, as point and line shapefiles.
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