The following variables need to be modified to activate nudging. The example shown below switches on nudging for horizontal winds
cat <<EOF >> user_nl_cam
!.......................................................
! Nudging setup
!.......................................................
Nudge_Model = .True.
Nudge_Path = '${path_nudging_data}'
Nudge_File_Template = '${casename}.h1.%y-%m-%d-00000.nc'
Nudge_Times_Per_Day = 4 !! nudging input data frequency
Model_Times_Per_Day = 48 !! should not be larger than 48 if dtime = 1800s
Nudge_Uprof = 1 !! 2 if nudging tendency has a vertical profile
Nudge_Ucoef = 1.
Nudge_Vprof = 1
Nudge_Vcoef = 1.
Nudge_Tprof = 0
Nudge_Tcoef = 0.
Nudge_Qprof = 0
Nudge_Qcoef = 0.
Nudge_PSprof = 0
Nudge_PScoef = 0.
Nudge_Beg_Year = 0001
Nudge_Beg_Month = 1
Nudge_Beg_Day = 1
Nudge_End_Year = 9999
Nudge_End_Month = 1
Nudge_End_Day = 1
Nudge_Vwin_Lindex = 0. !! activated only when Nudge_Xprof = 2 !! X = U, V, T
Nudge_Vwin_Hindex = 70. !! activated only when Nudge_Xprof = 2
Nudge_Vwin_Ldelta = 0.1. !! activated only when Nudge_Xprof = 2
Nudge_Vwin_Hdelta = 0.1. !! activated only when Nudge_Xprof = 2
Nudge_Vwin_lo = 0. !! activated only when Nudge_Xprof = 2
Nudge_Vwin_hi = 1. !! activated only when Nudge_Xprof = 2
Nudge_Method = 'Linear' !!
Nudge_Tau = 6. !! relaxation time scale, unit: h
Nudge_Loc_PhysOut = .True. !! nudging tendency calculated before radiation
Nudge_File_Ntime = 4 !! should be the same as Nudge_Times_Per_Day or 1 (see code for details)
Nudge_Allow_Missing_File = .False.
EOF
This setup will nudge the model towards a baseline E3SM simulation. The nudging data were created from the baseline simulation by archiving the 6-hourly meteorological fields. Only the horizontal winds are nudged, with a relaxation time scale of 6h. The nudging is applied at every grid box. More detailed information on how to setup a nudged simulation can be found in the source code nudging.F90.
To nudge the model towards a baseline model simulation (e.g. E3SMv1), you will need to run the reference model first and output U,V,T,Q,PS 6-hourly:
cat <<EOF >> user_nl_cam nhtfrq = 0,-6 mfilt = 1,1 fincl2 = ‘PS’,’U,’V’,’T’,’Q’, avgflag_pertape(2) = 'I' EOF
Under construction ...
- Sun, J., Zhang, K., Wan, H., Ma, P.-L., Tang, Q., Zhang, S. (2019), Impact of nudging strategy on the climate representativeness and hindcast skill of constrained EAMv1 simulations, Journal of Advances in Modeling Earth Systems, doi: 10.1029/2019MS001831.
- Zhang, K., Wan, H., Liu, X., Ghan, S. J., Kooperman, G. J., Ma, P.-L., Rasch, P. J., Neubauer, D., and Lohmann, U. (2014): Technical Note: On the use of nudging for aerosol–climate model intercomparison studies, Atmos. Chem. Phys., 14, 8631–8645, doi: 10.5194/acp-14-8631-2014.
- Zhang, S., Zhang, K., Wan, H., and Sun, J.: Further improvement and evaluation of nudging in the E3SM Atmosphere Model version 1 (EAMv1), Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2022-10, in review, 2022.
- Liu, Y., Zhang, K., Qian, Y., Wang, Y., Zou, Y., Song, Y., Wan, H., Liu, X., and Yang, X.-Q.: Investigation of short-term effective radiative forcing of fire aerosols over North America using nudged hindcast ensembles, Atmos. Chem. Phys., 18, 31–47, https://doi.org/10.5194/acp-18-31-2018, 2018.
- Lin, G., Wan, H., Zhang, K., Qian, Y., and Ghan, S. J. (2016), Can nudging be used to quantify model sensitivities in precipitation and cloud forcing?, J. Adv. Model. Earth Syst., 8, 1073-1091, https://doi.org/10.1002/2016MS000659.
- Kooperman, G. J., Pritchard, M. S., Ghan, S. J., Wang, M., Somerville, R. C. J., and Russell, L. M. (2012), Constraining the influence of natural variability to improve estimates of global aerosol indirect effects in a nudged version of the Community Atmosphere Model 5, J. Geophys. Res., 117, D23204, https://doi.org/10.1029/2012JD018588.