lib/xmet/skew_t.py

@@ -4,9 +4,12 @@ import cairo
 from typing import Callable
 
 from xmet.sounding import Sounding
-from xmet.thermo   import pressure_height, loft_parcel, moist_lapse_rate, \
-                          LAPSE_RATE_DRY, PRESSURE_MAX, PRESSURE_MIN, \
-                          PRESSURE_STEP
+from xmet.thermo   import pressure_height, lapse, moist_lapse_rate, \
+                          LAPSE_RATE_DRY
+
+PRESSURE_MAX  = 1050 # millibar
+PRESSURE_MIN  =  100
+PRESSURE_STEP =   50
 
 PRESSURE_LOG_MAX   = math.log(PRESSURE_MAX)
 PRESSURE_LOG_MIN   = math.log(PRESSURE_MIN)
@@ -104,11 +107,26 @@ class SkewTGraph():
                      start_temp: float,
                      start_pressure: float,
                      lapse_rate: Callable):
-        sx_last = None
-        sy_last = None
+        start_height = pressure_height(start_pressure)
+        sx_last      = None
+        sy_last      = None
+        height_last  = None
 
-        for level in loft_parcel(start_temp, start_pressure, lapse_rate):
-            temp, pressure = level
+        temp     = start_temp
+        pressure = start_pressure
+
+        while pressure >= PRESSURE_MIN:
+            height = pressure_height(pressure)
+
+            if height_last is None:
+                height_last = height
+
+            try:
+                rate = lapse_rate(temp, temp, pressure)
+            except OverflowError:
+                break
+
+            temp = lapse(temp, height - height_last, rate)
 
             sx, sy = self.sample_to_screen(temp, pressure)
 
@@ -117,8 +135,16 @@ class SkewTGraph():
                 cr.line_to(x + sx_last, y + sy_last)
                 cr.stroke()
 
-            sx_last = sx
-            sy_last = sy
+            sx_last     = sx
+            sy_last     = sy
+            height_last = height
+
+            if pressure == PRESSURE_MIN:
+                break
+            elif pressure - 10.0 < PRESSURE_MIN:
+                pressure = PRESSURE_MIN
+            else:
+                pressure -= 10.0
 
     def draw_adiabats(self,
                       cr: cairo.Context,

lib/xmet/thermo.py

@@ -1,12 +1,6 @@
-from typing import Callable
-
 LAPSE_RATE_DRY   = 9.8 / 1000 # degrees C per km
 LAPSE_RATE_MOIST = 4.0 / 1000
 
-PRESSURE_MAX  = 1050 # millibar
-PRESSURE_MIN  =  100
-PRESSURE_STEP =   50
-
 def kelvin(c: float) -> float:
     return 273.15 + c
 
@@ -73,45 +67,3 @@ def moist_lapse_rate(temp: float, dewpoint: float, pressure: float) -> float:
 
     return g * (1 + (Hv * r) / (Rsd * T)) \
              / (Cpd + (((Hv**2) * r) / (Rsw * (T**2))))
-
-def loft_parcel(start_temp: float,
-                start_pressure: float,
-                lapse_rate: Callable):
-    """
-    Loft a parcel of air from a given pressure, at a given temperature,
-    yielding a Tuple containing the temperature and pressure of that parcel
-    at each increment of elevation.  A Callable which, given a temperature,
-    dewpoint, pressure value, will be dispatched to obtain the lapse rate
-    for each height.
-    """
-    start_height = pressure_height(start_pressure)
-    sx_last      = None
-    sy_last      = None
-    height_last  = None
-
-    temp     = start_temp
-    pressure = start_pressure
-
-    while pressure >= PRESSURE_MIN:
-        height = pressure_height(pressure)
-
-        if height_last is None:
-            height_last = height
-
-        try:
-            rate = lapse_rate(temp, temp, pressure)
-        except OverflowError:
-            break
-
-        temp = lapse(temp, height - height_last, rate)
-
-        yield temp, pressure
-
-        height_last = height
-
-        if pressure == PRESSURE_MIN:
-            break
-        elif pressure - 10.0 < PRESSURE_MIN:
-            pressure = PRESSURE_MIN
-        else:
-            pressure -= 10.0