Climate Simulations
Introduction
The HARMONIE system can also be used for climate simulations: long, continuous runs, without data assimilation. This development started at SMHI and is now continued in the HCLIM consortium.
Some differences between NWP and climate simulations
| NWP | climate | |
|---|---|---|
| cycling | cycled runs (e.g. every 3hrs a 48hr run) | continuous runs |
| run length | few days | days - decades (centuries) |
| data assimilation | upper air and surface | none |
| boundaries | mostly IFS operational | ERA5, GCM, RCM, HCLIM |
| SST/SIC | constant during cycle | SST updated from boundary files |
| output format | GRIB | NetCDF |
| output files | per time step with all fields | per variable with all time steps |
Getting the code
Climate simulations can be performed using the regular HARMONIE system. The HCLIM repository contains specific adaptations and new developments for climate simulations.
Relevant settings
This paragraph gives an overview of the most important differences in settings between NWP and climate simulations.
ecf/config_exp.h
| variable | climate setting | meaning |
|---|---|---|
SIMULATION_TYPE | climsim | main switch for NWP/climate simulation, controls e.g. tdf file used and settings |
CISBA | DIF | Type of ISBA scheme in SURFEX |
CSNOW | 3-L | Type of snow scheme in SURFEX |
ANAATMO | none | upper air data assimilation |
ANASURF | none | surface data assimilation |
SSTSIC_UPD | yes | update SST/SIC from boundary files |
BDSTRATEGY | era5 | boundary strategy, ERA5 reanalysis data. Or use different value when downscaling a GCM |
NVGRIB | 2 | GRIB packing for atmosphere FA files, can be set to 0 to increase accuracy to avoid rounding errors when de-accumulating fields |
ARCHIVE_FORMAT | nc | format of archive files |
NCNAMES | climate | naming of netcdf variables |
Apart from the AROME physics, non-hydrostatic dynamics configuration, also experiments with ALADIN physics, with hydrostatic dynamics are run at resolutions of ca 12km.
nam/surfex_namelists.pm
| task | namelist | variable | climate setting | meaning |
|---|---|---|---|---|
| ISBA PREP | NAM_PREP_ISBA_SNOW | 12 | NSNOW_LAYER | number of snow layers |
| ISBA DIF | NAM_ISBA | CALBEDO | CM13 | albedo type |
| FORECAST | NAM_ISBAn | CSNOWRES | RIL | Maximum Richardson number limit for stable conditionsISBA-SNOW3L turbulent exchange option |
Running
Running is similar to regular Harmonie runs, but an end DTG must be specified:
Harmonie start DTG=2015120100 DTGEND=2021010100 [-c AROME_CLIMSIM|ALADIN_CLIMSIM]This will use the climsim.tdf playfile to load the ecFlow suite and perform all the required tasks:
- installation
- climate file generation
- boundary file generation
- run the forecast
- convert FA to netcdf
- archive output
- clean
While the Harmonie start command does everything, optionally the compilation and climate file generation steps can be run separately with Harmonie install and Harmonie climate, respectively. Climate simulations run in blocks of one month. Each new month is started from the last history and full SURFEX files of the previous month.
Input data
Climate files
HCLIM uses the same imput data for climate file generation as Harmonie.
Boundary files
ERA re-analysis data
When running on ECWMF, ERA-Interm or ERA5 data can be retrieved automatically from MARS.
CMIP GCM
GCM NetCDF files from CMIP5/CMIP6 need to be converted to ECMWF-like GRIB-files first. The CMIPtoHCLIM tool can be used for this conversion.
RACMO
RACMO asimof files can be handled by HCLIM directly. Set HOST_MODEL=racmo, SST_SOURCES=RACMO.
Greenhouse gas data
Harmonie by default uses the SRES A1B scenarios for greenhouse gases. In the HCLIM repository code has been backported from CY48 to update greenhouse gases from netcdf files, and the CMIP6 SSP370 scenario is used as default. See greenhouse gases for more info.
Output
The raw output of HCLIM is FA. But instead of converting to FA files to GRIB, HCLIM typically converts to NetCDF. Also, the files are reorganised from file per time step with all variables, to files per variable with all time steps. Accumulated fields are de-accumulated and converted to fluxes by default. The output in the HCLIM repository is tailored to meet the requirements of the CORDEX6 projects as much as possible. See the File Formats page for more info. A full list of all default HCLIM output is shown in this sheet.