Plot wind speed

I'm assuming the default colormap is in knots

Author: dnerini

src/plotting/colormap_defaults.py

@@ -15,9 +15,9 @@ def _fallback():
     "sp": {"cmap": plt.get_cmap("coolwarm", 11), "vmin": 800 * 100, "vmax": 1100 * 100},
     "2d": load_ncl_colormap("t2m_29lev.ct"),
     "2t": load_ncl_colormap("t2m_29lev.ct") | {"units": "degC"},
-    "10v": load_ncl_colormap("uv_17lev.ct") | {"units": "m/s"},
-    "10u": load_ncl_colormap("uv_17lev.ct") | {"units": "m/s"},
-    "uv": load_ncl_colormap("uv_17lev.ct"),
+    "10v": load_ncl_colormap("uv_17lev.ct") | {"units": "kt"},
+    "10u": load_ncl_colormap("uv_17lev.ct") | {"units": "kt"},
+    "10sp": load_ncl_colormap("uv_17lev.ct") | {"units": "kt"},
     "10si": {"cmap": plt.get_cmap("GnBu", 11), "vmin": 0, "vmax": 25},
     "t_850": {"cmap": plt.get_cmap("inferno", 11), "vmin": 220, "vmax": 310},
     "z_850": {"cmap": plt.get_cmap("coolwarm", 11), "vmin": 8000, "vmax": 17000},

workflow/Snakefile

@@ -52,7 +52,7 @@ rule showcase_all:
             / "showcases/{run_id}/{init_time}/{init_time}_{param}_{projection}_{region}.gif",
             init_time=[t.strftime("%Y%m%d%H%M") for t in REFTIMES],
             run_id=collect_all_runs(),
-            param="2t",
+            param=["2t", "10sp"],
             projection="orthographic",
             region=["none", "switzerland"],
         ),

workflow/scripts/plot_forecast_frame.mo.py

@@ -80,7 +80,13 @@ def _(ArgumentParser, Path):
 def _(grib_dir, init_time, lead_time, load_state_from_grib, param):
     # load grib file
     grib_file = grib_dir / f"{init_time}_{lead_time}.grib"
-    state = load_state_from_grib(grib_file, paramlist=[param])
+    if param == "10sp":
+        paramlist = ["10u", "10v"]
+    elif param == "sp":
+        paramlist = ["u", "v"]
+    else:
+        paramlist = [param]
+    state = load_state_from_grib(grib_file, paramlist=paramlist)
     return (state,)
 
 
@@ -120,17 +126,27 @@ def _k_to_c(arr):
             except Exception:
                 return arr - 273.15
 
+        def _ms_to_knots(arr):
+            # robust conversion with pint, fallback if dtype unsupported
+            try:
+                return (_ureg.Quantity(arr, _ureg.meter / _ureg.second).to(_ureg.knot)).magnitude
+            except Exception:
+                return arr * 1.943844
+
     except Exception:
-        LOG.warning("pint not available; falling back to K->C by subtracting 273.15")
+        LOG.warning("pint not available; falling back hardcoded conversions")
 
         def _k_to_c(arr):
             return arr - 273.15
 
+        def _ms_to_knots(arr):
+            return arr * 1.943844
+
     def preprocess_field(param: str, state: dict):
         """
         - Temperatures (2t, 2d, t, d): K -> °C
-        - Wind speed at 10m (10sp): sqrt(10u^2 + 10v^2)
-        - Wind speed (sp): sqrt(u^2 + v^2)
+        - Wind speed at 10m (10sp): m/s -> kn, sqrt(10u^2 + 10v^2)
+        - Wind speed (sp): m/s -> kn, sqrt(u^2 + v^2)
         Returns: (field_array, units_override or None)
         """
         fields = state["fields"]
@@ -139,18 +155,14 @@ def preprocess_field(param: str, state: dict):
             return _k_to_c(fields[param]), "°C"
         # 10m wind speed (allow legacy 'uv' alias)
         if param == "10sp":
-            u = fields.get("10u")
-            v = fields.get("10v")
-            if u is None or v is None:
-                raise KeyError("Required components 10u/10v not in state['fields']")
-            return np.sqrt(u**2 + v**2), "m s$^{-1}$"
+            u = _ms_to_knots(fields["10u"])
+            v = _ms_to_knots(fields["10v"])
+            return np.sqrt(u**2 + v**2), "kn"
         # wind speed from standard-level components
         if param == "sp":
-            u = fields.get("u")
-            v = fields.get("v")
-            if u is None or v is None:
-                raise KeyError("Required components u/v not in state['fields']")
-            return np.sqrt(u**2 + v**2), "m s$^{-1}$"
+            u = _ms_to_knots(fields["u"])
+            v = _ms_to_knots(fields["v"])
+            return np.sqrt(u**2 + v**2), "kn"
         # default: passthrough
         return fields[param], None
     return (preprocess_field,)