een the k-1 and k levels
             the values diff_m(:,:,1) and diff_m(:,:,1) are not used

         p_half -- real, dimension(:,:,:)
             pressure at interface between model levels
             size(p_half,3) must = 1 + size(t,3)
             units = Pascals

         p_full -- real, dimension(:,:,:)
             pressure at full model levels
             size(p_half,3) must = size(t,3)
             units = Pascals

         z_full -- real, dimension(:,:,:)
             height of the levels wher