How to configure a nudged simulation using E3SM

Nudging configuration (for E3SMv2)

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.

Creating nudging files from a baseline simulation

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

Creating nudging files from reanalysis

Under construction ...

References

• 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.