Format of files: All grids are in GRAVSOFT (scanline) format.
Data are stored in E-W rows from N to S. 
The header (latS,latN,lonW,lonE,dlat,dlon) defines limits in degrees.
The first point in file is thus (latN,lonW), last value (latS, lonE).
Main ArcGP grids contain:
312 rows and 4320 columns (5'x5') or 
312 rows and 2160 columns (5'x10')

*Remember:  If you change platforms (Windows/Unix) between the download and 
the running of the data, check for extra characters (i.e. ^M).


Generic Fortran code to read grids:
dimension row(4320)
read(*,*) rlat1,rlat2,rlon1,rlon2,dlat,dlon
nn = (rlat2-rlat1)/dlat+1.5
ne = (rlon2-rlon1)/dlon+1.5
rlat = rlat2
do i = 1, nn
  read(*,*) (row(j),j=1,ne)
  rlon = rlon1
  do j = 1,ne
    if (rlon .gt. 360) rlon = rlon1
    write(*,*) rlat, rlon, row(j)
    rlon = rlon + dlon
  enddo
  rlat = rlat - dlat
enddo
