GETM

About GETM

The General Estuarine Transport Model is a 3D structured grid model particularly suited for coastal applications.

Using GETM with FABM

GETM implements support for FABM on top of GOTM. Thus, settings provided through gotm_fabm.nml apply to GETM as well. Additionally, GETM reads the file getm_fabm.nml with GETM-specific settings. This file typically contains:

&getm_fabm_nml
   fabm_init_method=1,
   fabm_init_file='fabm_fields.nc',
   fabm_init_format=2,
   fabm_field_no=1,
   fabm_adv_hor=4
   fabm_adv_ver=4
   fabm_adv_split=1
   fabm_AH=-1.
/

These settings are described in the following table:

parameter	interpretation	default
fabm_init_method	Method to initialize FABM state variables: 0 = from hotstart file, 1 = use FABM-provided values across the entire spatial domain, 2 = read from NetCDF file	0
fabm_init_file	Path to file with initial values for FABM state variables (used only with fabm_init_method=2)
fabm_init_format	Format of file with initial values for FABM state variables (used only with fabm_init_method=2). Supported values: 2 = NetCDF.
fabm_field_no	Time index from which to read initial state (used only with fabm_init_method=2).
fabm_adv_hor	Numerical scheme to solve horizontal advection equation: 0 = advection disabled, 1 = upstream (first-order, monotone), 2 = 2DH-upstream with forced monotonicity, 3 = P2 (third-order, non-monotone), 4 = TVD-Superbee (second-order, monotone), 5 = TVD-MUSCL (second-order, monotone), 6 = TVD-P2-PDM or ULTIMATE QUICKEST (third-order, monotone), 8 = 2DH-FCT, 9 = 2DH-P2	1
fabm_adv_ver	Numerical scheme to solve vertical advection equation (transport only; the method to solve residual vertical movement by biogeochemical tracers is configured in gotm_fabm.nml). The following options are available: 0 = advection disabled, 1 = upstream (first-order, monotone), 3 = P2 (third-order, non-monotone), 4 = TVD-Superbee (second-order, monotone), 5 = TVD-MUSCL (second-order, monotone), 6 = TVD-P2-PDM or ULTIMATE QUICKEST (third-order, monotone)	1
fabm_adv_split	Method used to split 3D advection equation: 0 = no splitting (one 3D uvw step), 1 = full step splitting (u + v + w), 2 = half step splitting (u/2 + v/2 + w + v/2 + u/2), 3 = horizontal/vertical splitting (uv + w)	0
fabm_AH	Horizontal diffusivity (m2 s-1). Set to a negative value to disable horizontal diffusion altogether (the default). If a positive value is provided, it applies across the entire spatial domain.

Best practice: In order to prevent non-negative biogeochemical tracers from taking on negative values, a monotonicity-preserving numerical scheme must be used for advection. Further, to achieve consistent simulations, it is recommended to use the same numerical schemes for all tracers, that is, for temperature, salinity and biogeochemistry. Therefore, it is recommended to set fabm_adv_hor equal to the values of salt_adv_hor and temp_adv_hor (configured in getm.inp), to set fabm_adv_ver equal to salt_adv_ver and temp_adv_ver, to set fabm_adv_split equal to the values of salt_adv_split and temp_adv_split, and to set fabm_AH equal to salt_AH and temp_AH.