[mpas-developers] a bug in the SW code in the trunk

[Chen, Qingshan]

Hi everyone,

I think I have found a bug in the SW code in the trunk. On lines 126 and 129 of mpas_sw_time_integration.F, the halo update for divergence and vorticity for computation of del4 diffusion is done for the time_level 2. However it only makes sense to update these two variables for provis, since it is provis that is used to compute the tendencies. 

This part of code was copied, most likely by me, from the ocean core. I have checked and seen that this bug has been fixed in the ocean core. If everyone agrees with me, then I would like to take the responsibility and fix this bug in the SW core. Since it is a very simple fix, I will likely just do it in the trunk and then commit the changes. 

Thanks!
Qingshan