# ICON glossary

###### tags: `ICON`

ICON uses many terms and "standard" abrevations in its variable namings not all of them are obvious.

## Terms glossary

| Name | Translation/Fullname | Description |
| -------- | -------- | -------- |
| RBF | **r**adial **b**asis **f**unctions | Functions that depend only on Euclidian distances of points |
| btraj | **back trajectory**||
| \_bdy\_ | **boundary**|used as abreviation in many variable names|
|enh_ | **enh**anced | example would be *enh_smag_fac* = enhanced Smagorinski factor. |
| interface levels| **vertical half levels**| In comments/documentation they often talk about model *interface levels* to denot the vertical half levels. |
|\_ddt\_ | *time derivative: d/dt* | used as part of variable names, f.ex. `ddt_w_adv_pc`, many of these fields are kept in diagnostic state in ICON|
|iau | **i**ncrement **a**nalysis **u**pdate | tendencies from data assimilation are incorporated into to model |
| _me | layer **m**iddle (?) on **e**dge | | |
| _ic_ | layer **i**nterface at **c**ell center |||
| pc | predictor-corrector |||
| apc | *please define* (from mo_velocity_advection) |||
| pgr | pressure gradient |||
| \_expl\_ | explicit |||
| \_impl\_ | implicit |||
| \_ubc\_ | upper boundary condition |||
| \_pr | perturbation or 'prime' |stands for perturbation or prime since \prime notation is used in mathematical papers to denote the perturbations|
| _grf\_ | grid refinement |||
| bdywidth | boundary width |||
| _rcf_ | reduced calling frequency |||

## Important variables and concepts

|Name| Type |Description | Location|
|---|---|---|---|
|`nproma`|integer| block size in general of cells, but used for all dimensions (cells, edges, vertices). First (fastest running) index in ICON fields. | mo_parallel_config.f90 |
|`t_patch`|Fortran derived type | contains the grid information in an array instance (1 to the number of nested domains) `p_patch` passed as parameter to subroutines. It is a large structure containing grid and decomposition information |mo_model_domain.f90|
|`w`|field(nproma,nlevp1,nblks_c), part of prognostic variables (`t_nh_prog`)|orthogonal (to cell centers) vertical wind [m/s]|mo_nonhydro_state.f90|
|`vn`|field(nproma,nlev,nblks_e), part of prognostic variables (`t_nh_prog`)|orthogonal normal (to edges) wind) [m/s]|mo_nonhydro_state.f90|
|`rho`|field(nproma,nlev,nblks_c), part of prognostic variables (`t_nh_prog`)|density [kg/m^3]|mo_nonhydro_state.f90|
|`exner`|field (nproma,nlev,nblks_c), part of prognostic variables (`t_nh_prog`)|exner pressure, [-] dimensionless |mo_nonhydro_state.f90|
|`theta_v`|field(nproma,nlev,nblks_c), part of prognostic variables (`t_nh_prog`)|virtual potential temperature, [K] ) |mo_nonhydro_state.f90|
|`vt`|field(nproma,nlev,nblks_e) part of diagnostics (`t_nh_diag`)|tangential (to edges) wind [m/s]|mo_nonhydro_state.f90|
|`exner_pr`|field (nproma,nlev,nblks_c) part of diagnostics (`t_nh_diag`)|exner pressure *perturbation* [-], saved from previous step|mo_nonhydro_state.f90|