The second version of the gridded dataset is ageographic (lat/long) format. Basically the data gives the mean accumulation in kg/m2/year in 1-degree boxes.
To get it I have created a lat/long graticule to lay over the original grid. I have calculated the mean accumulation for each lat/long box as the mean of the values on the original grid that fall into each lat/long box.
At the coast, where some lat/long boxes contain mixed and sea , the new value is the mean of the land points only. Thus if you integrate for total accumulation over the continent using the two grids you will get different answers.
To help you overcome any problems with this I have also noted the fraction of each lat/long boxes which is sea (in grid terms). This sea fraction is also given for each box.
Where the sea fraction is 1.00 (all sea) the accumulation rate is set to -9999 ie a null value
The format is