Adds notes about generating ELM land IC

components/elm/docs/user-guide/index.md

@@ -76,3 +76,8 @@ Using the above-mentioned settings:
 [FATES](fates.md) can be run in various modes with ELM through the use of namelist settings.
 The [FATES User's Guide section on namelist options](https://fates-users-guide.readthedocs.io/en/latest/user/Namelist-Options-and-Run-Time-Modes.html)
 provides guidance on enabling these different FATES run modes.
+
+
+## Generate land initial condition
+
+Initial ELM condition can be generated using `interpinic` and the notes about it are available [here](interpinic.md).

components/elm/docs/user-guide/interpinic.md

@@ -0,0 +1,80 @@
+# Creating an ELM initial condition file
+
+An ELM initial condition (IC) file can be created by remapping an existing IC file from
+one resolution to another using the `interpinic`, located at
+`components/elm/tools/interpinic`. An ELM IC file is in the same format as an ELM restart file.
+The composet of the remapped IC file will be the same as that of the input IC file.
+So, for a new ELM SP-mode IC file, use an ELM input file corresponding to the SP-mode.
+
+The steps involved in creating a new IC files are as follows:
+
+1. Identifying an input ELM IC or restart file that will be remapped.
+2. Obtaining an ELM restart file at the new resolution.
+3. Compiling `interpinic` on the machine of interest.
+4. Running `interpinic` to perform the interpolation.
+
+The notes below provide an example of creating 1850 ELM IC file for the NARRM grid using E3SM v3 LR piControl from year = 0101. These notes are provided for Chrysalis.
+
+
+### 1. Identification of the input ELM IC file
+
+The identified input land condition file for this case is the following:
+
+```
+/lcrc/group/e3sm2/ac.golaz/E3SMv3/v3.LR.piControl/archive/rest/0101-01-01-00000/v3.LR.piControl.elm.r.0101-01-01-00000.nc
+```
+
+### 2. Obtaining an ELM restart file
+
+Using an existing NARRM land IC and making a copy of it
+
+```
+cd components/elm/tools/interpinic
+
+cp /lcrc/group/e3sm/data/inputdata/lnd/clm2/initdata_map/elmi.v3-NARRM.northamericax4v1pg2_r025_IcoswISC30E3r5.1870-01-01-00000.c20240704.nc \
+elmi.v3-NARRM.northamericax4v1pg2_r025_IcoswISC30E3r5.1850-01-01-00000.c`date "+%Y%m%d"`.nc
+```
+
+### 3. Compiling `interpinic`
+
+```
+# Load relevant modules.
+cd <e3sm-dir>
+eval $(./cime/CIME/Tools/get_case_env/get_case_env)
+
+#
+cd components/elm/tools/interpinic/src
+
+export USER_LDFLAGS="-L$NETCDF_C_DIR/lib -lnetcdf -L$NETCDF_F_DIR/lib -lnetcdff  -L$HDF5_DIR/lib -lhdf5"
+
+USER_FC=ifort LIB_NETCDF="`nc-config --flibs`" INC_NETCDF="`nf-config --includedir`" make VERBOSE=1
+
+```
+
+
+### 4. Run `interpinic`
+
+The `interpinic ` can then be run via the following batch job (e.g., `remap.r025_RRSwISC6to18E3r4.1850.batch`) to generate the initial condition.
+
+```
+>cat remap.r025_RRSwISC6to18E3r4.1850.batch
+
+#!/bin/sh
+#SBATCH  --job-name=remap
+#SBATCH  --nodes=1
+#SBATCH  --exclusive
+#SBATCH  --time 24:00:00
+#SBATCH  -p slurm
+#SBATCH  --account esmd
+
+# Load relevant modules.
+cd <e3sm-dir>
+eval $(./cime/CIME/Tools/get_case_env/get_case_env)
+
+# Change dir to `interpinic`
+cd components/elm/tools/interpinic/src
+
+srun -n 1 ./interpinic \
+-i /lcrc/group/e3sm2/ac.golaz/E3SMv3/v3.LR.piControl/archive/rest/0101-01-01-00000/v3.LR.piControl.elm.r.0101-01-01-00000.nc \
+-o elmi.v3-NARRM.northamericax4v1pg2_r025_IcoswISC30E3r5.1850-01-01-00000.c20240903.nc
+```