Biharmonic horizontal mixing.

The biharmonic mixing coefficients for tracers ah and momentum am are specified in separate namelists. The defaults shown in the namelists are only valid for a particular grid size; the user must determine the appropriate values for their particular grid size. The variable_hmix option modifies the coefficients ah and am based on functions of the grid cell areas and will reduce the values for smaller grid cells (am and ah thus represent the values at the largest grid cells). Currently, the functional form of this scaling can only be changed by editing the modules. The auto_hmix option attempts to compute coefficients based on known values for other resolutions. The result may or may not be suitable and the auto_hmix option is provided mainly for flexible benchmarking of the code at various resolutions.

Table: Biharmonic momentum mixing namelist

&hmix_del4u_nml	LANL default	CESM1 dipole-grid default	CESM1 tripole-grid default	Valid values	Biharmonic momentum mixing parameters
lauto_hmix	.false.	.false.	.false.	.true., .false.	compute mixing coefficient based on resolution
lvariable_hmix	.true.	.false.	.true.	.true., .false.	scale mixing coeff by grid cell area
am	-0.6 x 1020	-0.6 x 1020	-27 x 1017		momentum mixing coeff (cm2/s)
/

Table: Biharmonic tracer mixing namelist

&hmix_del4t_nml	LANL default	CESM1 dipole-grid default	CESM1 tripole-grid default	Valid values	Biharmonic tracer mixing parameters
lauto_hmix	.true.	.false.	.false.	.true., .false.	compute mixing coefficient based on resolution
lvariable_hmix	.true.	.false.	.true.	.true., .false.	scale mixing coeff by grid cell area
ah	~-0.2 x 1020	~-0.2 x 1020	-3.0 x 1017		tracer mixing coefficient (cm2/s)
/