# GRIST#

**Provided by** Chinese Academy of Meteorological Sciences (CAMS), China

## Model description#

GRIST is a unified model system for global weather and climate modeling. Its dynamical core solves the primitive equations but with the vertical acceleration term restored for nonhydrostatic modeling (Zhang et al. 2019; Zhang et al. 2020). The horizontal grid is fully unstructured and uses the Voronoi-style polygon as the primal cell.

The 5-km, nonhydrostatic global model configuration for DYAMOND Winter experiment is a simplified version of the setup used by Zhang et al. (2021). In particular, no cumulus parameterization (shallow, deep) was used.

## Experiment runs#

### GRIST 5km atmosphere-only#

- Location:
`/fastdata/ka1081/DYAMOND/data/winter_data/CAMS/GRIST-5km/DW-ATM/`

- Setup:
Atmosphere-only, with land model is Noah-MP. SST and sea ice concentration are prescribed.

- Resolution:
The horizontal resolution is 5 km (23592962 cells), based on 9-time recursive bisection of a regular icosahedron with a final-step trisection (G9B3).

The vertical resolution is 30 layers with a top at 2.25 hPa (~40 km).

The nominal model time step is 60 s.

- Comments:
The atmosphere initial condition comes from IFS-analysis data. The land model is initialized using ERA5 data. SST and sea ice are prescribed.

For post-processing the GRIST data, we recommend using CDO to first interpolate the unstructured-mesh data to a regular global (or regional) lat-lon grid. The vertical interpolation can be done using any linear interpolation function.

**Please note:**Because GRIST uses a dry-air-mass-based vertical coordinate, please do not use the typical \(hyam*p_0 + hybm*p_s\) approach for reconstructing (moist) hydrostatic pressure at each model level (or any function that assumes this relationship). One may use`mpressureFace`

in the model output for vertical interpolation to a constant pressure level.

- Contact person:

### GRIST 5km coupled#

- Location:
`/fastdata/ka1081/DYAMOND/data/winter_data/CAMS/GRIST-5km/DW-CPL/`

- Setup:
Atmosphere-Land-Ocean-Sea Ice coupled. The atmospheric model is GRIST, the land model is Noah-MP. The oceanic model is MOM6, the sea ice model is SIS2.

- Resolution:
The horizontal resolution of the atmospheric model is 5 km (23592962 cells), based on 9-time recursive bisection of a regular icosahedron with a final-step trisection (G9B3). The vertical resolution is 30 layers with a top at 2.25 hPa (~40 km). The nominal model time step is 60 s.

The nominal horizontal resolution of the oceanic model is 0.05° (7200x5400 cells): a Mercator grid spans from 65°S to 60°N with 7200×3500 cells, a bipolar cap following Murray (1996) covers north of 60°N with 7200×1200 cells, a spherical grid from 78°S to 65°S with 7200×550 cells, and a displaced pole grid sits south of 78°S with 7200×150 cells. The vertical resolution is 75 layers. The oceanic baroclinic dynamics time step is 180 s, with the thermodynamic and tracer advection time step of 360 s. The slow ice dynamics time step is 180 s, the sub-cycling time step for iterating the rheology and ice momentum equations is 20 s. The coupled time step within the oceanic model is 360 s, which means that the time step of the fast sea ice process is 60 s and the coupled period between fast sea ice and slow ice dynamics/ocean dynamics is 360 s.

- Comments:
The atmosphere initial condition comes from IFS-analysis data. The land model is initialized using ERA5 data.

For post-processing the non-standardized GRIST data, we recommend using CDO to first interpolate the unstructured-mesh data to a regular global (or regional) lat-lon grid. The vertical interpolation can be done using any linear interpolation function.

**Please note:**Because GRIST uses a dry-air-mass-based vertical coordinate, please do not use the typical \(hyam*p_0 + hybm*p_s\) approach for reconstructing (moist) hydrostatic pressure at each model level (or any function that assumes this relationship). One may use`mpressureFace`

in the model output for vertical interpolation to a constant pressure level.The oceanic initial condition comes from an OMIP2-type simulation of the stand-alone ocean-sea ice model, forcing with the JRA55-do data: the model was firstly spin-up for 2 years with climatological forcing, starting for a rest ocean and climatological WOA13 temperature and salinity data, then forced with the JRA55-do data from 2019-01-01 to 2020-01-19 to produce the initial condition at 2020-01-20.

Noting that as MOM6 uses a tripolar horizontal grid north of 60°N, the users are recommended to first using CDO to interpolate the scalar data to a regular lon-lat grid, using the 2D lon-lat grid information of the model (

`geo_lonlat.nc`

file). For the vector data north of 60°N, it may need to first rotate the vector according to the angle between the generalized curve coordinates and the lon-lat direction then apply interpolation.The vertical velocity data is not provided as MOM6 uses a hybrid depth-isopycnal vertical coordinate with the Lagrangian-remap method, with which the vertical velocity is hard to precisely diagnosed.

- Contact person:
Xinyao Rong (CMA Earth System Modeling and Prediction Center（CEMC）and CAMS)