Support for Fields in multiple files without a time dimension

This PR fixes #1831

Author: erikvansebille

parcels/field.py

@@ -684,12 +684,17 @@ def from_netcdf(
         if grid is None:
             # Concatenate time variable to determine overall dimension
             # across multiple files
-            time, time_origin, timeslices, dataFiles = cls._collect_timeslices(
-                timestamps, data_filenames, _grid_fb_class, dimensions, indices, netcdf_engine
-            )
-            grid = Grid.create_grid(lon, lat, depth, time, time_origin=time_origin, mesh=mesh)
-            grid.timeslices = timeslices
-            kwargs["dataFiles"] = dataFiles
+            if "time" in dimensions:
+                time, time_origin, timeslices, dataFiles = cls._collect_timeslices(
+                    timestamps, data_filenames, _grid_fb_class, dimensions, indices, netcdf_engine
+                )
+                grid = Grid.create_grid(lon, lat, depth, time, time_origin=time_origin, mesh=mesh)
+                grid.timeslices = timeslices
+                kwargs["dataFiles"] = dataFiles
+            else:  # e.g. for the CROCO CS_w field, see https://github.com/OceanParcels/Parcels/issues/1831
+                grid = Grid.create_grid(lon, lat, depth, np.array([0.0]), time_origin=TimeConverter(0.0), mesh=mesh)
+                grid.timeslices = [[0]]
+                data_filenames = [data_filenames[0]]
         elif grid is not None and ("dataFiles" not in kwargs or kwargs["dataFiles"] is None):
             # ==== means: the field has a shared grid, but may have different data files, so we need to collect the
             # ==== correct file time series again.