id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
466	IMPORTANT: horizontal viscosity and MIX_GEO_UV	arango	arango	"Checking the horizontal viscosity along geopotentials ('''MIX_GEO_UV''') has been in my to-do list for very long time. We have some complains about this in the past about the model blowing-up in parallel applications and arrays out-of-range in couple of DO-loops. I checked this problem and I was able to reproduce the reported problems.

I corrected the parallel bugs for '''uv3dmix2_geo.h''' and '''uv3dmix4_geo.h'''.  Also corrected a missing '''dt''' factor in the biharmonic mixing.

I did an analysis for each do loop and reworked all the DO-loop ranges and eliminated specifying them with local CPP directives. I wrote then in such a way that eliminated special treatment in nesting applications.

I also revised and tested the tangent linear, representer, and adjoint version of these routines.  I also added the new code for time-evolving, 3D viscosity coefficients. However, this time evolving capability is not yet available in adjoint-based applications.  It is coded for completeness and availability in the future.

Many thanks to Xinyou Lin for [https://www.myroms.org/forum/viewtopic.php?f=19&t=1685 bringing] this to my attention.

Although the '''MIX_GEO_UV''' option is rarely used for momentum. I highly recommend everybody to update because this is an important correction and this bug has been in ROMS for long time."	bug	closed	major	Release ROMS/TOMS 3.4	Nonlinear	3.4	Fixed