update periodicBC to stay within longitudinal limits

Author: reint-fischer

tests/test_advection.py

@@ -464,7 +464,7 @@ def test_nemo_curvilinear_fieldset():
     runtime = np.timedelta64(160, "D")
 
     def periodicBC(particles, fieldset):  # pragma: no cover
-        particles.dlon = np.where(particles.lon > 180, particles.dlon - 360, particles.dlon)
+        particles.dlon = np.where(particles.lon + particles.dlon > 180, particles.dlon - 360, particles.dlon)
 
     pset = parcels.ParticleSet(fieldset, lon=lonp, lat=latp)
     pset.execute([AdvectionEE, periodicBC], runtime=runtime, dt=np.timedelta64(6, "h"))