Halo exchange hangs for high-order W0 field on multigrid mesh in high-res runs #239
Description
Orography is set in gungho by specifying the surface_altitude field, which is a 2D W0 field. This field is then used to modify the vertical values of the chi fields.
The chi fields are never halo exchanged, and their modification is performed up to the full mesh halo depth. But to do this, we must perform a halo exchange on the surface_altitude field up to its full halo depth.
For large numbers of procs (e.g. 2000), when I increase the order of finite element for the surface_altitude field, I have found that the halo exchange hangs for the coarsest multigrid mesh and does not complete.
I have a workaround in #238 which keeps the coordinate order for multigrid meshes at 1