cube_to_target performs rigourous remapping of topo variables from cubed-sphere grid to 
any target grid. In the process SGH is computed.

Input files:

1. USGS-topo-cube.nc (may be found here $CESMDATA/inputdata/atm/cam/hrtopo/USGS-topo-cube3000.nc)

   This is the topo data on a cubed-sphere (default is 3km cubed-sphere grid)

2. target.nc (e.g., $CESMDATA/inputdata/atm/cam/grid-description/se/ne30np4_091226_pentagons.nc)

   This is a SCRIP/ESMF grid descriptor file for the target grid

3. phis-smooth.nc

   (optional) The user may provide a smoothed PHIS field. The software then recomputes SGH to
   account for the smoothing in the sub-grid-scale. 



