Values of ice extent are stored as millions of square kilometers and are calculated by summing 
the total area of all grid boxes that contain at least 15% of ice.

Values of ice area are stored as millions of square kilometers and are calculated by weighting the area of
each grid box by the concentration, and then summing together for all grid boxes that contain at least 15% 
of ice. Ice area is always lower than extent for a given ice concentration field.

WARNING: Other sea ice data sets are likely to contain different land/sea masks. This significantly affects 
the values of extent and area, so please take this into consideration during any comparisons.

The number of fields (rows) is stored at the start of each file on the first line. 

The year, month and the extent/area is then stored on each line (row).

Example:

12
1850   1  13.16
1850   2   9.23
1850   3   8.07
1850   4  14.90
1850   5  17.31
1850   6  20.75
1850   7  23.24
1850   8  25.10
1850   9  28.02
1850  10  24.59
1850  11  21.40
1850  12  17.30