Initial implementation of shear calculation

lib/xmet/sounding.py

@@ -1,3 +1,4 @@
+import math
 import datetime
 import shapely
 
@@ -11,7 +12,11 @@ from xmet.thermo import follow_dry_adiabat, \
                         follow_saturated_mixing_ratio, \
                         pressure_height, \
                         virtual_temp, \
-                        kelvin
+                        kelvin, \
+                        wind_u, \
+                        wind_v
+
+from xmet.units import deg
 
 LAPSE_RATE_DRY   = 9.8 # degrees C per 1000m
 LAPSE_RATE_MOIST = 4.0
@@ -204,6 +209,26 @@ class Sounding(DatabaseTable):
 
         return series
 
+    def shear(self, level: int):
+        s1 = self.samples[level]
+        s2 = self.samples[level+1]
+
+        u1 = wind_u(s1.wind_speed, s1.wind_dir)
+        u2 = wind_u(s2.wind_speed, s2.wind_dir)
+
+        v1 = wind_v(s1.wind_speed, s1.wind_dir)
+        v2 = wind_v(s2.wind_speed, s2.wind_dir)
+
+        zd = s2.height - s1.height
+
+        ud = (u2 - u1) / zd
+        vd = (v2 - v1) / zd
+
+        return (
+            ((ud**2 + vd**2)**0.5) / zd,
+            90 - deg(math.atan(vd / ud))
+        )
+
 def between(n, a, b):
     return n > a and n < b