                         dissipative_heat, Tri_surf,                      &
                          kbot)

    input: 

         is, js -- integers
             the location in the global lon-lat grid of the rectangular
             domain on which diffusion is to be performed
             the size of the domain is determined by the size ofthe input
             i.e, longitude index ranges from is to is + size(t,1) -1
                   latitude index ranges from js to js + size(t,2) -1

         delt -- 