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Draft for adding support for saturation water vapour over ice #2323

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Draft for adding support for saturation water vapour over ice #2323

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348d17c
Draft for adding support for saturation water vapour over ice
joernu76 Feb 1, 2022
9f85919
fixed flake8
joernu76 Feb 1, 2022
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59 changes: 41 additions & 18 deletions src/metpy/calc/thermo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@
@exporter.export
@preprocess_and_wrap(wrap_like='temperature', broadcast=('temperature', 'dewpoint'))
@check_units('[temperature]', '[temperature]')
def relative_humidity_from_dewpoint(temperature, dewpoint):
def relative_humidity_from_dewpoint(temperature, dewpoint, phase='liquid'):
r"""Calculate the relative humidity.

Uses temperature and dewpoint to calculate relative humidity as the ratio of vapor
Expand Down Expand Up @@ -56,8 +56,8 @@ def relative_humidity_from_dewpoint(temperature, dewpoint):
Renamed ``dewpt`` parameter to ``dewpoint``

"""
e = saturation_vapor_pressure(dewpoint)
e_s = saturation_vapor_pressure(temperature)
e = saturation_vapor_pressure(dewpoint, phase)
e_s = saturation_vapor_pressure(temperature, phase)
return (e / e_s)


Expand Down Expand Up @@ -996,7 +996,7 @@ def vapor_pressure(pressure, mixing_ratio):
@exporter.export
@preprocess_and_wrap(wrap_like='temperature')
@process_units({'temperature': '[temperature]'}, '[pressure]')
def saturation_vapor_pressure(temperature):
def saturation_vapor_pressure(temperature, phase='liquid'):
r"""Calculate the saturation water vapor (partial) pressure.

Parameters
Expand All @@ -1023,16 +1023,36 @@ def saturation_vapor_pressure(temperature):
.. math:: 6.112 e^\frac{17.67T}{T + 243.5}

"""
# Converted from original in terms of C to use kelvin.
return mpconsts.nounit.sat_pressure_0c * np.exp(
17.67 * (temperature - 273.15) / (temperature - 29.65)
)

def liquid(temperature):
# Converted from original in terms of C to use kelvin.
return mpconsts.nounit.sat_pressure_0c * np.exp(
17.67 * (temperature - 273.15) / (temperature - 29.65)
)

def ice(temperature):
# Alduchov and Eskridge (1996)
return mpconsts.nounit.sat_pressure_0c * np.exp(
22.587 * (temperature - 273.16) / (temperature + 0.7)
)

if phase == 'liquid':
return liquid(temperature)
elif phase == 'ice':
return ice(temperature)
else:
assert phase == 'temperature-dependent'
alpha = np.zeros_like(temperature, dtype=float)
t_sel = (temperature > 250.16) & (temperature < 273.16)
alpha[t_sel] = ((temperature[t_sel] - 250.16) / (273.16 - 250.16)) ** 2
alpha[temperature >= 273.16] = 1
return alpha * liquid(temperature) + (1 - alpha) * ice(temperature)


@exporter.export
@preprocess_and_wrap(wrap_like='temperature', broadcast=('temperature', 'relative_humidity'))
@check_units('[temperature]', '[dimensionless]')
def dewpoint_from_relative_humidity(temperature, relative_humidity):
def dewpoint_from_relative_humidity(temperature, relative_humidity, phase='liquid'):
r"""Calculate the ambient dewpoint given air temperature and relative humidity.

Parameters
Expand All @@ -1059,7 +1079,7 @@ def dewpoint_from_relative_humidity(temperature, relative_humidity):
"""
if np.any(relative_humidity > 1.2):
warnings.warn('Relative humidity >120%, ensure proper units.')
return dewpoint(relative_humidity * saturation_vapor_pressure(temperature))
return dewpoint(relative_humidity * saturation_vapor_pressure(temperature, phase))


@exporter.export
Expand Down Expand Up @@ -1158,7 +1178,7 @@ def mixing_ratio(partial_press, total_press, molecular_weight_ratio=mpconsts.nou
{'total_press': '[pressure]', 'temperature': '[temperature]'},
'[dimensionless]'
)
def saturation_mixing_ratio(total_press, temperature):
def saturation_mixing_ratio(total_press, temperature, phase='liquid'):
r"""Calculate the saturation mixing ratio of water vapor.

This calculation is given total atmospheric pressure and air temperature.
Expand Down Expand Up @@ -1187,7 +1207,8 @@ def saturation_mixing_ratio(total_press, temperature):
Renamed ``tot_press`` parameter to ``total_press``

"""
return mixing_ratio._nounit(saturation_vapor_pressure._nounit(temperature), total_press)
return mixing_ratio._nounit(saturation_vapor_pressure._nounit(
temperature, phase), total_press)


@exporter.export
Expand Down Expand Up @@ -1576,7 +1597,8 @@ def psychrometric_vapor_pressure_wet(pressure, dry_bulb_temperature, wet_bulb_te
broadcast=('pressure', 'temperature', 'relative_humidity')
)
@check_units('[pressure]', '[temperature]', '[dimensionless]')
def mixing_ratio_from_relative_humidity(pressure, temperature, relative_humidity):
def mixing_ratio_from_relative_humidity(
pressure, temperature, relative_humidity, phase='liquid'):
r"""Calculate the mixing ratio from relative humidity, temperature, and pressure.

Parameters
Expand Down Expand Up @@ -1615,7 +1637,7 @@ def mixing_ratio_from_relative_humidity(pressure, temperature, relative_humidity

"""
return (relative_humidity
* saturation_mixing_ratio(pressure, temperature)).to('dimensionless')
* saturation_mixing_ratio(pressure, temperature, phase)).to('dimensionless')


@exporter.export
Expand All @@ -1624,7 +1646,7 @@ def mixing_ratio_from_relative_humidity(pressure, temperature, relative_humidity
broadcast=('pressure', 'temperature', 'mixing_ratio')
)
@check_units('[pressure]', '[temperature]', '[dimensionless]')
def relative_humidity_from_mixing_ratio(pressure, temperature, mixing_ratio):
def relative_humidity_from_mixing_ratio(pressure, temperature, mixing_ratio, phase='liquid'):
r"""Calculate the relative humidity from mixing ratio, temperature, and pressure.

Parameters
Expand Down Expand Up @@ -1661,7 +1683,7 @@ def relative_humidity_from_mixing_ratio(pressure, temperature, mixing_ratio):
Changed signature from ``(mixing_ratio, temperature, pressure)``

"""
return mixing_ratio / saturation_mixing_ratio(pressure, temperature)
return mixing_ratio / saturation_mixing_ratio(pressure, temperature, phase)


@exporter.export
Expand Down Expand Up @@ -1736,7 +1758,8 @@ def specific_humidity_from_mixing_ratio(mixing_ratio):
broadcast=('pressure', 'temperature', 'specific_humidity')
)
@check_units('[pressure]', '[temperature]', '[dimensionless]')
def relative_humidity_from_specific_humidity(pressure, temperature, specific_humidity):
def relative_humidity_from_specific_humidity(
pressure, temperature, specific_humidity, phase='liquid'):
r"""Calculate the relative humidity from specific humidity, temperature, and pressure.

Parameters
Expand Down Expand Up @@ -1774,7 +1797,7 @@ def relative_humidity_from_specific_humidity(pressure, temperature, specific_hum

"""
return (mixing_ratio_from_specific_humidity(specific_humidity)
/ saturation_mixing_ratio(pressure, temperature))
/ saturation_mixing_ratio(pressure, temperature, phase))


@exporter.export
Expand Down