The generic_advdiff package contains high-level subroutines to solve the advection-diffusion equation of any tracer, either active (potential temperature, salinity or water vapor) or passive (see :ref:`pkg/ptracer <sub_phys_pkg_ptracers>`). (see also :numref:`tracer_eqns` and :numref:`advection_schemes`).
Package “generic_advdiff” provides a common set of routines for calculating advective/diffusive fluxes for tracers (cell centered quantities on a C-grid).
Many different advection schemes are available: the standard centered second order, centered fourth order and upwind biased third order schemes are known as linear methods and require some stable time-stepping method such as Adams-Bashforth. Alternatives such as flux-limited schemes are stable in the forward sense and are best combined with the multi-dimensional method provided in :filelink:`gad\_advection <pkg/generic_advdiff/gad_advection.F>`.
There are two high-level routines:
- :filelink:`GAD\_CALC\_RHS <pkg/generic_advdiff/gad_calc_rhs.F>` calculates all fluxes at time level “n” and is used for the standard linear schemes. This must be used in conjuction with Adams–Bashforth time stepping. Diffusive and parameterized fluxes are always calculated here.
- :filelink:`GAD\_ADVECTION <pkg/generic_advdiff/gad_advection.F>` calculates just the advective fluxes using the non-linear schemes and can not be used in conjuction with Adams–Bashforth time stepping.
.. tabularcolumns:: |\Y{.4}|L|L|
| CPP Flag Name | Default | Description |
|---|---|---|
| :varlink:`COSINEMETH_III` | #define | sets the implementation form of \cos{\varphi} scaling of bi-harmonic terms for tracer diffusivity (note, in :filelink:`pkg/generic_advdiff` routines the definition set here overrides whether this is defined in :filelink:`model/inc/CPP_OPTIONS.h`, where the setting affects viscous term calculations) |
| :varlink:`ISOTROPIC_COS_SCALING` | #undef | selects isotropic scaling of harmonic and bi-harmonic terms when using the \cos{\varphi} scaling (note, in :filelink:`pkg/generic_advdiff` routines the definition set here overrides whether this is defined in :filelink:`model/inc/CPP_OPTIONS.h`, where the setting affects viscous term calculations) |
| :varlink:`DISABLE_MULTIDIM_ADVECTION` | #undef | disables compilation of multi-dim. advection code |
| :varlink:`GAD_MULTIDIM_COMPRESSIBLE` | #undef | use compressible flow method for multi-dim advection instead of older, less accurate method; note option has no effect on SOM advection which always uses compressible flow method |
| :varlink:`GAD_ALLOW_TS_SOM_ADV` | #undef | enable the use of 2nd-order moment advection scheme (Prather 1986 :cite:`prather:86`) for temp. and salinity |
| :varlink:`GAD_SMOLARKIEWICZ_HACK` | #undef | enables hack to get rid of negatives caused by Redi, see Smolarkiewicz (1989) :cite:`smolark:89` (for ptracers, except temp and salinity) |
------------------------------------------------------------------------ <-Name->|Levs|<-parsing code->|<-- Units -->|<- Tile (max=80c) ------------------------------------------------------------------------ ADVr_TH | 15 |WM LR |degC.m^3/s |Vertical Advective Flux of Pot.Temperature ADVx_TH | 15 |UU 087MR |degC.m^3/s |Zonal Advective Flux of Pot.Temperature ADVy_TH | 15 |VV 086MR |degC.m^3/s |Meridional Advective Flux of Pot.Temperature DFrE_TH | 15 |WM LR |degC.m^3/s |Vertical Diffusive Flux of Pot.Temperature (Explicit part) DIFx_TH | 15 |UU 090MR |degC.m^3/s |Zonal Diffusive Flux of Pot.Temperature DIFy_TH | 15 |VV 089MR |degC.m^3/s |Meridional Diffusive Flux of Pot.Temperature DFrI_TH | 15 |WM LR |degC.m^3/s |Vertical Diffusive Flux of Pot.Temperature (Implicit part) ADVr_SLT| 15 |WM LR |(g/kg).m^3/s |Vertical Advective Flux of Salinity ADVx_SLT| 15 |UU 094MR |(g/kg).m^3/s |Zonal Advective Flux of Salinity ADVy_SLT| 15 |VV 093MR |(g/kg).m^3/s |Meridional Advective Flux of Salinity DFrE_SLT| 15 |WM LR |(g/kg).m^3/s |Vertical Diffusive Flux of Salinity (Explicit part) DIFx_SLT| 15 |UU 097MR |(g/kg).m^3/s |Zonal Diffusive Flux of Salinity DIFy_SLT| 15 |VV 096MR |(g/kg).m^3/s |Meridional Diffusive Flux of Salinity DFrI_SLT| 15 |WM LR |(g/kg).m^3/s |Vertical Diffusive Flux of Salinity (Implicit part)
- Baroclinic gyre experiment, in :filelink:`tutorial\_baroclinic\_gyre <verification/tutorial_baroclinic_gyre>` verification directory.
- Tracer Sensitivity tutorial, in :filelink:`tutorial\_tracer\_adjsens <verification/tutorial_tracer_adjsens>` verification directory.