How to perform nudging simulations with the regional refined model (RRM)

This guide assumes that one has successfully run the regional refined simulation following the instructions (https://acme-climate.atlassian.net/wiki/display/ATM/Configuring%2C+building%2C+and+running+regionally+refined+CONUS+grid).

Step-by-step guide

1. Create the analysis fields on the RRM grids
   
   1. Interpolate the analysis fields (e.g., ECMWF, NCEP, MERRA, and etc.) to the RRM grid.
   2. The nudging code (ACME/models/atm/cam/src/physics/cam/nudging.F90) is developed by Patrick Callaghan. The code can nudge the model states of U, V, T, Q, and/or PS in the physics module.
   3. It is important, in some cases, to account for the differences in the topography used in the source analysis data and that for a specific RRM configuration.
   4. If interested in the analysis fields used for the RRM-CONUS nudging simulation, please contact Qi Tang.
2. Specify the nudging parameters
   1. The nudging parameters can be specified in the user_nl_cam.
   2. Details about the parameters are given in nudging.F90
3. An updated version of example is documented in a recent GMD paper (Tang et al., 2019).

An example of nudging U and V outside the CONUS domain in the simulation for the CSSEF project is provided below:

&nudging_nl

 Nudge_Model        =.true.

 Nudge_Path         ='/gpfs/mira-fs0/projects/HiRes_Climate/qtang/Nudging/SE/INTERIM/arm_30_x8.g/2011/'

 Nudge_File_Template='interim_se_%y%m%d00_%y%m%d18_TQUV.nc'

 Nudge_Times_Per_Day=4

 Model_Times_Per_Day=144

 Nudge_Uprof  =2

 Nudge_Ucoef  =1.00

 Nudge_Vprof  =2

 Nudge_Vcoef  =1.00

 Nudge_Tprof  =0

 Nudge_Tcoef  =0.00

 Nudge_Qprof  =0

 Nudge_Qcoef  =0.00

 Nudge_PSprof =0

 Nudge_PScoef =0.00

 Nudge_Beg_Year =2011

 Nudge_Beg_Month=1

 Nudge_Beg_Day  =1

 Nudge_End_Year =2011

 Nudge_End_Month=8

 Nudge_End_Day  =31

 Nudge_Hwin_lo      =1.0

 Nudge_Hwin_hi      =0.0

 Nudge_Hwin_lat0    =38.

 Nudge_Hwin_latWidth=34. 

 Nudge_Hwin_latDelta=3.8

 Nudge_Hwin_lon0    =254.

 Nudge_Hwin_lonWidth=44. 

 Nudge_Hwin_lonDelta=3.8

 Nudge_Vwin_lo      =0.0

 Nudge_Vwin_hi      =1.0

 Nudge_Vwin_Hindex  =31.

 Nudge_Vwin_Hdelta  =0.1

 Nudge_Vwin_Lindex  =0.

 Nudge_Vwin_Ldelta  =0.1

/

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