Imperfect restarts
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In trying to debug what we thought was an OBC issue, I have found a problem in the vertical viscosity on tile boundaries on restart. Running through an hour on 24 cores vs running after reading the one hour restart on four cores shows differences in visc_rem_u on a tile boundary. I have tracked it as far as a_cpl coming out of find_coupling_coef. More tomorrow, perhaps.
visc%KV_shear is on h points, but is averaged across u points for KV_add. It has an out of date value in the halo.
MOM_diabatic_driver.F90 has a pass_var for Kv_shear on line 410, then Kv_shear gets stuff added to it later in the routine.
Sorry, no, that doesn't explain anything. Line 410 is after the diabatic_ALE and friends get called where the changes happen. It's debugger time again.
I have found it - we need a pass_var after remap_vertvisc_aux_vars.
This has been fixed.