def sh2ppmv(q, p):
"""Convert specific humidity [kg/kg] to parts per million by volume ppmv
required for RTTOV
Parameters
----------
q specific humidity [kg/kg]
p air pressure [Pa]
Returns
-------
pressure [ppmv]
"""
# Gas Konstanten trocken / feucht
c = con.eps() # Parameters()['Rd']/Parameters()['Rv']
# Dampfdruck
r = q / (1 - q)
# r mixing ratio
# c is Rd/Rv
# aus e = r p /(r+c)
e = r * p / (c + r)
# e = (q * p)/(q + (1 - q)*c)
# Volumen-spez.
# 10e6 * Pwater / (Ptotal - Pwater)
return 1e6 * (e / (p - e))
def vap2sh(e, p):
""" Convert water vapor pressure to specific humidity
Parameters
----------
e Water vapor [Pa]
p air pressure [Pa]
Returns
-------
specific humidity in kg/kg
"""
c = con.eps() # Rd/Rv
Pd = p - e
return (e * c) / (e * c + Pd)
def sh2vap(q, p):
"""Specific Humidity to Water vapor pressure
Parameters
----------
q specific humidity [kg/kg]
p air pressure [Pa]
Returns
-------
water vapor pressure [Pa]
"""
c = con.eps() # Rd / Rv
return (q * p) / (q + (1 - q) * c)
