Gent-McWilliams (gent) mixing operates only on tracer species (potential temperature, salinity and other tracers), so it should be used in conjunction with a different option for hmix_momentum_choice, typically either del2 or aniso. No bi-harmonic form of gent has been developed and accepted yet, so it is appropriate to use the del2 values of ah. For vertical dependence of the mixing, a profile with the form κ1 + κ2 exp(-z/D) can be chosen, where D is a depth scale, z is model depth and κ1 and κ2 parameters specifiy factors multiplying the diffusivity. Note that this function is multiplied by the diffusivity ah; for a constant κ the first parameter should be set to 1 and the second to 0. Two diffusivities can be specified for the Redi and bolus parts of the GM parameterization; ah is used for the Redi part, ah_bolus is used for the bolus part. Two different maximum slopes can also be specified to allow different taperings of the Redi and bolus terms. A backgroud horizontal diffusivity ah_bkg can be used for bottom cells. If the gm_bolus flag is set, the bolus velocity is explicitly calculated and used as part of the velocity field, as opposed to the incorporating this process as part of the horizontal mixing. This last option does not currently work with partial bottom cells.
| &hmix_gm_nml | Valid values [LANL default] |
Gent-McWilliams isopycnic diffusion |
| kappa_choice | ['constant'], 'variable' | constant or (horizontally) variable kappa |
| slope_control_choice | ['notanh'], 'tanh', 'clip', 'gerdes' | control slope using tanh, algebraic approximation to tanh (notanh), clipping or method of Gerdes |
| kappa_depth_1 | [1.0] | the first term in the function for variation of kappa with depth |
| kappa_depth_2 | [0.0] | the coefficient of the exponential in the function for variation of kappa with depth |
| kappa_depth_scale | [150000.0] | the depth scale for the exponential in the function for variation of kappa with depth |
| ah | [0.8 x 107] | diffusion coeff for Redi part (cm2/s) |
| ah_bolus | [0.8 x 107] | diffusion coeff for bolus part (cm2/s) |
| [ah_bkg] | [0.0] | diffusion coeff for bottom cells (cm2/s) |
| slm_r | 0.01 | max slope for Redi terms |
| slm_b | 0.01 | max slope for bolus terms |
| [gm_bolus] | .true., [.false.] | option for explicit calculation of bolus velocity |
| / |
| &hmix_gm_nml | CESM1 gx3 dipole-grid default | CESM1 gx1 dipole-grid default | CESM1 tripole-grid default | Valid values | Gent-McWilliams isopycnic diffusion |
| kappa_isop_choice | 'bfre' | 'bfre' | 'bfre' | 'bfre', 'edgr', 'cons', 'dept', 'vmhs', 'hdgr', 'drad', 'bfvm', 'bfhd', 'bfdr' | choice for KAPPA_ISOP |
| kappa_thic_choice | 'bfre' | 'bfre' | 'bfre' | 'bfre', 'edgr', 'cons', 'dept', 'vmhs', 'hdgr', 'drad', 'bfvm', 'bfhd', 'bfdr' | choice for KAPPA_THIC |
| kappa_freq_choice | 'once_a_day' | 'once_a_day' | 'once_a_day' | 'once_a_day', 'never', 'every' | frequency choice for kappa computation (once a day, never, every timestep) |
| slope_control_choice | 'notanh' | 'notanh' | 'notanh' | 'notanh', 'tanh', 'clip', 'gerdes' | control slope using tanh, algebraic approximation to tanh (notanh), clipping or method of Gerdes |
| kappa_depth_1 | 1.0 | 1.0 | 1.0 | the first term in the function for variation of kappa with depth | |
| kappa_depth_2 | 0.0 | 0.0 | 0.0 | the coefficient of the exponential in the function for variation of kappa with depth | |
| kappa_depth_scale | 150000.0 | 150000.0 | 150000.0 | CESM1 scripts determine value based upon resolution and other option settings | the depth scale for the exponential in the function for variation of kappa with depth |
| ah | 4.0e7 | 3.0e7 | 3.0e7 | CESM1 scripts determine value based upon resolution and other option settings | diffusion coeff for Redi part (cm2/s) |
| ah_bolus | 4.0e7 | 3.0e7 | 3.0e7 | CESM1 scripts determine value based upon resolution and other option settings | diffusion coeff for bolus part (cm2/s) |
| use_const_ah_bkg_srfbl | .true. | .true. | .true. | .true., .false. | if .true., then the specified constant value of ah_bkg_srfbl is used as the "maximum" background horizontal diffusivity within the surface boundary layer. Otherwise, KAPPA_ISOP is utilized as this "maximum". |
| ah_bkg_srfbl | 4.0e7 | 3.0e7 | 3.0e7 | automatically set by CESM1 scripts, depending on resolution and options selected | backgroud horizontal diffusivity within the surface boundary layer |
| ah_bkg_bottom | 0.0 | 0.0 | 0.0 | backgroud horizontal diffusivity within the surface boundary layer | |
| slm_r | 0.03 | 0.03 | 0.03 | max slope for Redi terms | |
| slm_b | 0.03 | 0.03 | 0.03 | max slope for bolus terms | |
| diag_gm_bolus | .true. | .true. | .false. | .true.,.false. | if .true., compute diagnostic bolus velocity |
| transition_layer_on | .true. | .true. | .true. | .true., .false. | if .true., use transition layer parameterization |
| read_n2_data | .false. | .false. | .false. | .true., .false. | if .true., use climatological N2 data instead of model dependent N2 |
| buoyancy_freq_filename | 'bouyancy_freq' | 'bouyancy_freq' | 'bouyancy_freq' | character string <= 256 chars | file name for the time-independent buoyancy frequency squared |
| buoyancy_freq_fmt | 'nc' | 'nc' | 'nc' | 'nc', 'bin' | file format suffix for the buoyancy_freq_filename file |
| const_eg | 1.2 | 1.2 | 1.2 | tuning parameter (unitless) | |
| gamma_eg | 500.0 | 500.0 | 500.0 | effective upper limit for inverse eddy time scale (unitless) | |
| kappa_min_eg | 0.35 x 107 | 0.35 x 107 | 0.35 x 107 | minimum KAPPA (cm2/s) | |
| kappa_max_eg | 2.0 x 107 | 2.0 x 107 | 2.0 x 107 | maximum KAPPA (cm2/s) | |
| / |
| &mix_submeso_nml | CESM1 default | Valid values | submesoscale eddies |
| efficiency_factor | 0.07 | (0.6,0.8) | efficiency factor |
| time_scale_constant | 8.64e4 | (8.64e4,7*2.64e4) | time-scale constant (s) |
| luse_const_horiz_len_scale | .false. | .true., .false. | if .true., use constant horizontal length scale. if .false., hor_length_scale is used as the lower limit |
| hor_length_scale | 5.0e5 | horizontal length scale (cm) | |
| / |
The user is referred to the The Parallel Ocean Program (POP) Reference Manual for details on the various options listed in the CESM1 POP2 hmix_gm_nml and mix_submeso_nml namelists.
2010-04-01