Fixing diffusion tutorial

Author: erikvansebille

docs/user_guide/examples/tutorial_diffusion.ipynb

@@ -265,7 +265,6 @@
    "outputs": [],
    "source": [
     "testParticles = get_test_particles()\n",
-    "testParticles.update_dt_dtype(\"timedelta64[ms]\")\n",
     "output_file = parcels.ParticleFile(\n",
     "    store=\"M1_out.zarr\",\n",
     "    chunks=(len(testParticles), 50),\n",
@@ -345,7 +344,6 @@
    "outputs": [],
    "source": [
     "testParticles = get_test_particles()\n",
-    "testParticles.update_dt_dtype(\"timedelta64[ms]\")\n",
     "output_file = parcels.ParticleFile(\n",
     "    store=\"EM_out.zarr\",\n",
     "    chunks=(len(testParticles), 50),\n",
@@ -458,8 +456,12 @@
     "    A = A / sq_deg_to_sq_m\n",
     "    Kh = fieldset.Cs * A * np.sqrt(dudx**2 + 0.5 * (dudy + dvdx) ** 2 + dvdy**2)\n",
     "\n",
-    "    dlat = np.random.normal(0.0, 1.0, dt.shape) * np.sqrt(2 * np.fabs(dt) * Kh)\n",
-    "    dlon = np.random.normal(0.0, 1.0, dt.shape) * np.sqrt(2 * np.fabs(dt) * Kh)\n",
+    "    dlat = np.random.normal(0.0, 1.0, particles.dt.shape) * np.sqrt(\n",
+    "        2 * np.fabs(particles.dt) * Kh\n",
+    "    )\n",
+    "    dlon = np.random.normal(0.0, 1.0, particles.dt.shape) * np.sqrt(\n",
+    "        2 * np.fabs(particles.dt) * Kh\n",
+    "    )\n",
     "    particles.dlat += dlat\n",
     "    particles.dlon += dlon"
    ]

src/parcels/_core/particleset.py

@@ -633,7 +633,7 @@ def _get_simulation_start_and_end_times(
 
 def _get_start_time(first_release_time, time_interval, sign_dt, runtime):
     if time_interval is None:
-        time_interval = TimeInterval(np.timedelta64(0, "s"), right=np.timedelta64(int(runtime), "s"))
+        time_interval = TimeInterval(np.timedelta64(0, "s"), right=np.timedelta64(int(runtime * 1e9), "ns"))
 
     if sign_dt == 1:
         fieldset_start = 0.0