array(72,46,12)
unit: Gg (giga gram)
spatial resolution: 4x5 latitude and longitude
grid arrangement
 (sample code to calculate longitude(Glon) and latitude(Glat) using IDL)
   for j = 0, 45 do begin
   for i = 0, 71 do begin
      Glon(i, j) = -180. + i * 5.
      if ( j eq 0 ) then begin
         Glat(i, j) = -89.00
      endif else if ( j eq 45  ) then begin 
         Glat(i, j) =  89.00
      endif else begin
         Glat(i, j) = -86.00 + (j-1) * 4.
      endelse
  endfor
  endfor