Add logic to identify if it is necessary to interpolate the extpar file.

templates/event-generator/interpolate_sst.sh

 function interpolate_SST() {
-  local GRID_FILE="$1"
+  local DYNAMICS_GRID_FILE="$1"
   local SST_INPUT="$2"
   local SST_OUTPUT="$3"
 
@@ -9,7 +9,7 @@ function interpolate_SST() {
   &remap_nml
   in_filename = "${SST_INPUT}"
   in_type = 1
-  out_grid_filename = "${GRID_FILE}"
+  out_grid_filename = "${DYNAMICS_GRID_FILE}"
   out_filename = "${SST_OUTPUT}"
   out_type = 2
   out_filetype = 4
@@ -31,27 +31,46 @@ END
 
 }
 
+#!/bin/bash
+
+# Define the function
+function grid_filename_from_extpar() {
+  # Assuming the filename is given as the first argument to the function
+  filename="$1"
+
+  # This extracts the grid identifier from the filename
+  grid_id="${filename:12:12}"
+
+  # This constructs the new filename
+  grid_filename="icon_grid_${grid_id}.nc"
+
+  # This prints out the new filename
+  echo "${grid_filename}"
+}
+
 function interpolate_extpar() {
 
-  local GRID_FILE="$1"
+  local DYNAMICS_GRID_FILE="$1"
   local EXTERNAL_PARAMETERS_FILE="$2"
 
   echo "Converting extpar file to ICON grid"
 
-  cat >remap.nml <<END
+  EXTERNAL_PARAMETERS_GRID_FILE=$(grid_filename_from_extpar ${EXTERNAL_PARAMETERS_FILE})
 
+  if [ "${DYNAMICS_GRID_FILE}" != "${EXTERNAL_PARAMETERS_GRID_FILE}" ]; then
+    cat >remap.nml <<END
 &remap_nml
 in_filename = "${EXTERNAL_PARAMETERS_FILE}"
-in_grid_filename = "${EXTERNAL_PARAMETERS_GRID}"
+in_grid_filename = "${EXTERNAL_PARAMETERS_GRID_FILE}"
 in_type = 2
-out_grid_filename = "${GRID_FILE}"
+out_grid_filename = "${DYNAMICS_GRID_FILE}"
 out_filename = "extpar.nc"
 out_type = 2
 out_filetype = 4
 /
 END
 
-  cat <<END >extend_remap_namelist.py
+    cat <<END >extend_remap_namelist.py
 import xarray as xr
 
 with xr.open_dataset("${EXTERNAL_PARAMETERS_FILE}") as ds, open('remap.nml', 'a') as file:
@@ -64,11 +83,14 @@ with xr.open_dataset("${EXTERNAL_PARAMETERS_FILE}") as ds, open('remap.nml', 'a'
        file.write('/\n\n')
 END
 
-  python3 extend_remap_namelist.py
+    python3 extend_remap_namelist.py
 
-  ulimit -s unlimited
-  OMP_NUM_THREADS=1 iconremap --remap_nml remap.nml #-vvv
-  rm remap.nml
+    ulimit -s unlimited
+    OMP_NUM_THREADS=1 iconremap --remap_nml remap.nml #-vvv
+    rm remap.nml
+  else
+    ln -sf "${EXTERNAL_PARAMETERS_FILE}" "extpar.nc"
+  fi
 }
 #
 #