13. Nudged experiments
13.1. Step by step guide for setting up a nudged simulation
13.1.1. Create a new case
with a compset that supports nudging e.g. NFHISTnorpddmsbcsdyn, or
use your own compset and add:
-offline_dyn
to CAM_CONFIG_OPTS in env_build.xml after creating a case.
Note
IMPORTANT NOTE (2022.09.06).
In current NorESM and CESM versions, the -offline_dyn option deactivates CAM’s energy fixer because it would interfere with nudging of T (and possibly also Q). This behaviour may change in future versions of NorESM. To re-activate the use of the energy fixer for wind-only nudging, copy the source file components/cam/src/physics/cam/check_energy.F90 to SourceMods/src.cam/ and comment out the line
heat_glob = 0._r8
13.1.2. Meteorology
Modify user_nl_cam include information about the meteorology you want to nudge to
&metdata_nl
met_filenames_list = '/cluster/shared/noresm/inputdata/noresm-only/inputForNudging/ERA_f09f09_32L_days/ fileList2001-2015.txt'
met_data_file = '/cluster/shared/noresm/inputdata/noresm-only/inputForNudging/ERA_f09f09_32L_days/ 2014-01-01.nc'
met_filenames_list points to a txt-file that must include all the meteorological nudging data that will be used for the entire simulation. The met_data_file points to the file in this list that includes the starting date of your simulation. The example above shows how to point to ERA-Interim data, created by Inger Helene Hafsahl Karset (https://www.duo.uio.no/handle/10852/72779). You can also create your own model produced data (explanation further down in this document).
13.1.3. Nudging strength
Modify user_nl_cam to include information about the strength of the nudging:
met_rlx_time = 6
met_rlx_time is the relaxation time scale. If the timestep of the model is 0.5 hrs, a relaxation time scale of 6 corresponds to a nudging strength of 0.5/6 ~ 0.083 = 8.3 %, meaning that 8.3 % of the nudged component (for example the wind) comes from the value in the met_data_file, while 93.7 % will come from the model itself. It is recommended to set met_rlx_time to the same value as the time frequency of the nudging data.
13.1.4. Vertical levels
Modify user_nl_cam to include information about which levels in the vertical the nudging
should apply to
met_rlx_bot = 60
met_rlx_top = 70
met_rlx_bot_bot = 0
met_rlx_bot_top = 0
By using the values in the example above, nudging will be applied to all levels in the vertical. If met_rlx_bot_bot and met_rlx_bot_top is set to heights (given in km) above the bottom layer of the model (0 km), met_rlx_time will decrease exponentially from met_rlx_bot_top (where it will have the value of met_rlx_time) to met_rlx_bot_bot (where it will be zero from this level and all the way down to the ground). If you want to dampen or turn off the nudging intensity higher up, the same can be done to met_rlx_bot and met_rlx_top by setting these values to be lower in the atmosphere than the model top.
13.1.5. Nudging only winds and surface pressure
Modify user_nl_cam if you only want to nudge winds and surface pressure:
met_nudge_only_uvps = .true.
This is recommended when looking at aerosol-cloud interactions, especially when nudging to meteorology that is not produced by the model itself (Zhang et al., 2014).
13.1.6. Appropriate topography
Modify user_nl_cam to point to an appropriate topography file if nudging to meteorology
from ERA-Interim or other meteorology that is not produced by the model itself. It is the field named PHIS in the topography file that need to correspond to the source of the nudging data.
&cam_inparm bnd_topo = '/cluster/shared/noresm/inputdata/noresm-only/inputForNudging/ERA_f09f09_32L_days/ERA_bnd_topo_noresm2_20191023.nc'
13.1.7. Correct calender
If nudging to reanalysis data, CALENDAR in env_build.xml should be changed from NO_LEAP to GREGORIAN.
13.1.8. Correct start date
Modify env_run.xml to have the same RUN_STARTDATE as given in the met_data_file.
13.1.9. Ready-steady-go
You are now ready to setup, build and submit your case.
13.2. How to generate your own nudging inputdata
13.2.1. Create a case
Create a case you want to generate data from
13.2.2. Modify user_nl_cam
Modify user_nl_cam and/or other user namelists to output the preferred nudging data
&camexp
mfilt = 1, 4,
nhtfrq = 0, -6,
avgflag_pertape='A','I',
fincl2 ='PS','U','V','T'
The example above will output ordinary h0 monthly mean files, one pr month, but also h1-files with instantaneous values of PS, U, V and T every six hours, four pr file.
13.2.3. Move the nudging data to a preferred folder
Move the nudging data (the h1-files) over to a preferred folder and create a txt-file including
a list of all the nudging data files that later can be pointed to as met_filenames_list
ls -d -1 $PWD/*.h1.*.nc > fileList.txt
For more information, look into the file where most of the nudging code is found
/components/cam/src/NorESM/fv/metdata.F90
There are also other options for namelist modifications regarding nudging: https://docs.cesm.ucar.edu/models/cesm2/settings/current/cam_nml.html and search for met_
13.3. Available meteo fields for nudging
13.3.1. 0.9x1.25 horizontal resolution, 32 layers (for NorESM2 / CAM6-Nor)
- ERA_f09f09_32L_days
Original ERA data : Period : 2000-01-01 until 2016-01-31 Horizontal resolution : f09 (0.9x1.25) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/ERA_f09f09_32L_days Storage location : fram, betzy Contact person : Comment :
- AL/ERA_f09f09_32L_days
Original ERA data : ERA-Interim Period : 2016-01-01 until 2018-12-31 Horizontal resolution : f09 (0.9x1.25) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/AL/ERA_f09f09_32L_days Storage location : fram Contact person : Comment : Produced on Tetralith (copy of ERAI4NORESM)
- ERAI4NORESM
Original ERA data : ERA-Interim Period : 2013-01-01 until 2019-08-31 Horizontal resolution : f09 (0.9x1.25) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : /proj/bolinc/users/x_geoso/ERAI4NORESM Storage location : tetralith Contact person : anna@misu.su.se Comment : Identical to the data AL/ERA_f09f09_32L_days on Fram
13.3.2. 0.9x1.25 horizontal resolution, 30 layers (for NorESM1.2 / CAM5.3-Nor)
- ERA_f09f09_30L_days
Original ERA data : Period : 2000-01-01 until 2018-03-31 Horizontal resolution : f09 (0.9x1.25) Vertical resolution : L30 (30 layers) Available fields : PS, T, Q, U, V Use : for NorESM1.2 / CAM5.3-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/ERA_f09f09_30L_days Storage location : fram, betzy, tetralith Contact person : Comment :
- ERA5_enda_30L
Original ERA data : ERA5 Period : 2002-01-01 until 2018-10-31 Horizontal resolution : f09 (0.9x1.25) Vertical resolution : L30 (30 layers) Available fields : PS, T, Q, U, V Use : for NorESM1.2 / CAM5.3-Nor simulations Storage directory : /proj/bolinc/shared/data/noresm/inputForNudging/ERA5_enda_30L Storage location : tetralith Contact person : anna@misu.su.se Comment : Created by Lena Frey on Tetralith
13.3.3. 1.9x2.5 horizontal resolution, 32 layers (for NorESM2 / CAM6-Nor)
- ERA_f19_tn14
Original ERA data : Period : 2007-01-01 until 2013-12-31 Horizontal resolution : f19 (1.9x2.5) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/ERA_f19_tn14 Storage location : fram, betzy Contact person : Comment :
- z_ABG/ERA_f19_tn14
Original ERA data : Period : 2007-01-01 until 2013-12-31 Horizontal resolution : f19 (1.9x2.5) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : noresm-only/inputForNudging/z_ABG/ERA_f19_tn14 Storage location : betzy Contact person : Comment :
- AZ/ERA_f19_tn14
Original ERA data : Period : 2007-01-01 until 2013-12-31 Horizontal resolution : f19 (1.9x2.5) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : noresm-only/inputForNudging/AZ/ERA_f19_tn14 Storage location : betzy Contact person : Comment :
- ERA_f19_tn14_SH
Original ERA data : Period : 2007-01-01 until 2013-12-31 Horizontal resolution : f19 (1.9x2.5) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : noresm-only/inputForNudging/ERA_f19_tn14_SH Storage location : fram Contact person : Comment :
- SMB/ERA_f19_tn14_gte2014
Original ERA data : Period : 2014-01-01 until 2019-01-31 Horizontal resolution : f19 (2.5x1.9) Vertical resolution : L32 (32 layers) Available fields : PS, T, Q, U, V Use : for NorESM2 / CAM6-Nor simulations Storage directory : noresm-only/inputForNudging/SMB/ERA_f19_tn14_gte2014 Storage location : fram Contact person : Comment :
13.3.4. 1.9x2.5 horizontal resolution, 30 layers (for NorESM1.2 / CAM5.3-Nor)
- ERA_f19_f19_L30
Original ERA data : Period : 2000-01-01 until 2010-12-31 Horizontal resolution : f19 (1.9x2.5) Vertical resolution : L30 Available fields : PS, T, Q, U, V Use : for NorESM1.2 / CAM5.3-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/ERA_f19_f19_L30 Storage location : fram, betzy Contact person : Comment :
- ERA_f19_g16
Original ERA data : Period : 1999-01-01 until 2004-01-31 Horizontal resolution : f19 (2.5x1.9) Vertical resolution : L30 (30 layers) Available fields : PS, T, Q, U, V Use : for NorESM1.2 / CAM5.3-Nor simulations Storage directory : inputdata/noresm-only/inputForNudging/ERA_f19_g16 Storage location : fram Contact person : Comment :