Update parcels/fieldset.py

Co-authored-by: Erik van Sebille <[email protected]>

Author: VeckoTheGecko

parcels/fieldset.py

@@ -237,6 +237,7 @@ def from_copernicusmarine(ds: xr.Dataset):
             fields["V"].units = Geographic()
 
             if "W" in ds.data_vars:
+                ds["W"] -= ds["W"]  # Negate W to convert from up positive to down positive (as that's the direction of positive depth)
                 fields["W"] = Field("W", ds["W"], grid)
                 fields["UVW"] = VectorField("UVW", fields["U"], fields["V"], fields["W"])
             else: