diff --git a/python/extpar_era_to_buffer.py b/python/extpar_era_to_buffer.py
index dc5eb59a4..08c28a8ef 100755
--- a/python/extpar_era_to_buffer.py
+++ b/python/extpar_era_to_buffer.py
@@ -144,8 +144,13 @@
 logging.info('')
 
 # calculate weights
-utils.launch_shell('cdo', '-f', 'nc4', lock, '-P', omp, f'genycon,{grid}',
-                   tg.cdo_sellonlat(), raw_data_sst, weights)
+era_5_resolution = 31.0  # approximate ERA5 resolution [km]
+if (tg.resolution < era_5_resolution):
+    utils.launch_shell('cdo', '-f', 'nc4', lock, '-P', omp, f'genbil,{grid}',
+                       tg.cdo_sellonlat(), raw_data_sst, weights)
+else:
+    utils.launch_shell('cdo', '-f', 'nc4', lock, '-P', omp, f'genycon,{grid}',
+                       tg.cdo_sellonlat(), raw_data_sst, weights)
 
 # regrid SST
 utils.launch_shell('cdo', '-f', 'nc4', lock, '-P', omp,
diff --git a/python/lib/grid_def.py b/python/lib/grid_def.py
index a1c9aec4a..36d8b8db5 100644
--- a/python/lib/grid_def.py
+++ b/python/lib/grid_def.py
@@ -72,6 +72,9 @@ def __init__(self, namelist):
 
         self.lats, self.lons = self.latlon_cosmo_to_latlon_regular()
 
+        self.resolution = (
+            (2.0 * np.pi * 6.371229 * 10**3) / 360.0 * self.dlon)  # [km]
+
     def create_grid_description(self, name):
         '''
         write grid description required for cdo
@@ -263,6 +266,9 @@ def __init__(self, gridfile):
         self.vlons = np.rad2deg(self.grid.variables["vlon"][:])
         self.vlats = np.rad2deg(self.grid.variables["vlat"][:])
 
+        self.resolution = (
+            5050.0 / (self.grid.grid_root * 2**self.grid.grid_level))  # [km]
+
     def cdo_sellonlat(self, dlon=1.0, dlat=1.0):
         '''
         create the string for the cdo option "-sellonlatbox"