Use saturated mixing ratio in moist lapse rate

lib/xmet/thermo.py

@@ -19,21 +19,21 @@ def saturated_vapor_pressure(temp: float) -> float:
 
 def mixing_ratio(dewpoint: float, pressure: float) -> float:
     """
-    Return the amount, in grams, of water vapor versus dry air in a parcel of
-    a given dewpoint and pressure.
+    Return the amount, in kilograms, of water vapor versus dry air in a parcel
+    of a given dewpoint and pressure.
     """
     e = vapor_pressure(dewpoint)
 
-    return 621.97 * (e / (pressure - e))
+    return (0.62197 * e) / (pressure - e)
 
 def saturated_mixing_ratio(temp: float, pressure: float) -> float:
     """
-    Return the maximum amount, in grams, of water vapor a parcel of a given
-    temperature and pressure can hold.
+    Return the maximum amount, in kilograms, of water vapor a parcel of a
+    given temperature and pressure can hold.
     """
     es = saturated_vapor_pressure(temp)
 
-    return 621.97 * (es / (pressure - es))
+    return (0.62197 * es) / (pressure - es)
 
 def lcl(temp: float, dewpoint: float) -> float:
     """
@@ -59,11 +59,11 @@ def lapse(temp: float, delta: float, rate=LAPSE_RATE_DRY) -> float:
 def moist_lapse_rate(temp: float, dewpoint: float, pressure: float) -> float:
     g   = 9.8076
     Hv  = 2501000
-    r   = mixing_ratio(dewpoint, pressure)
     Rsd = 287
     Rsw = 461.5
     Cpd = 1003.5
+    r   = saturated_mixing_ratio(dewpoint, pressure)
     T   = kelvin(temp)
 
     return g * (1 + (Hv * r) / (Rsd * T)) \
-             / (Cpd + ((Hv**2 * r) / (Rsw * T**2)))
+             / (Cpd + (((Hv**2) * r) / (Rsw * (T**2))))