Moisture/temperature dependent gas constants & latent heat

docs/_templates/overrides/metpy.calc.rst

@@ -39,6 +39,9 @@ Moist Thermodynamics
       mixing_ratio
       mixing_ratio_from_relative_humidity
       mixing_ratio_from_specific_humidity
+      moist_air_gas_constant
+      moist_air_poisson_exponent
+      moist_air_specific_heat_pressure
       moist_lapse
       moist_static_energy
       precipitable_water
@@ -60,6 +63,9 @@ Moist Thermodynamics
       virtual_potential_temperature
       virtual_temperature
       virtual_temperature_from_dewpoint
+      water_latent_heat_melting
+      water_latent_heat_sublimation
+      water_latent_heat_vaporization
       wet_bulb_temperature
       wet_bulb_potential_temperature
 

docs/api/references.rst

@@ -2,6 +2,10 @@
 References
 ==========
 
+.. [Ambaum2020] Ambaum MHP, 2020: Accurate, simple equation for saturated vapour pressure over water and ice.
+           *QJR Meteorol Soc.*; **146**: 4252–4258,
+           doi: `10.1002/qj.3899 <https://doi.org/10.1002/qj.3899>`_.
+
 .. [Anderson2013] Anderson, G. B., M. L. Bell, and R. D. Peng, 2013: Methods to
            Calculate the Heat Index as an Exposure Metric in Environmental Health
            Research. *Environmental Health Perspectives*, **121**, 1111-1119,
@@ -176,6 +180,10 @@ References
 .. [Rochette2006] Rochette, Scott M., and Patrick S. Market. "A primer on the
                   ageostrophic wind." Natl. Weather Dig. 30 (2006): 17-28.
 
+.. [Romps2017] Romps, D. M., 2017: Exact Expression for the Lifting Condensation Level.
+            *J. Atmos. Sci.*, **74**, 3891–3900,
+            doi: `10.1175/JAS-D-17-0102.1. <https://doi.org/10.1175/JAS-D-17-0102.1.>`_.
+
 .. [Rothfusz1990] Rothfusz, L.P.: *The Heat Index "Equation"*. Fort Worth, TX: Scientific
            Services Division, NWS Southern Region Headquarters, 1990.
            `SR90-23 <../_static/rothfusz-1990-heat-index-equation.pdf>`_, 2 pp.

docs/conf.py

@@ -455,6 +455,7 @@
     # Couldn't fix these 403's with user agents
     r'https://doi\.org/10\.1029/2010GL045777',
     r'https://doi\.org/10\.1098/rspa\.2004\.1430',
+    r'https://doi\.org/10\.1002/qj\.3899',
     # Currently giving certificate errors on GitHub
     r'https://library.wmo.int/.*',
     # For some reason GHA gets a 403 from Stack Overflow

src/metpy/calc/thermo.py

@@ -29,6 +29,251 @@
 exporter = Exporter(globals())
 
 
+@exporter.export
+@preprocess_and_wrap(wrap_like='specific_humidity')
+@process_units(input_dimensionalities={'specific_humidity': 'dimensionless'},
+               output_dimensionalities='[specific_heat_capacity]',
+               output_to='J K**-1 kg**-1 ')
+def moist_air_gas_constant(specific_humidity):
+    r"""Calculate R_m, the specific gas constant for a parcel of moist air.
+
+    Parameters
+    ----------
+    specific_humidity : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Specific gas constant
+
+    Examples
+    --------
+    >>> from metpy.calc import moist_air_gas_constant
+    >>> from metpy.units import units
+    >>> moist_air_gas_constant(11 * units('g/kg'))
+    <Quantity(288.966723, 'joule / kelvin / kilogram')>
+
+    See Also
+    --------
+    moist_air_specific_heat_pressure, moist_air_poisson_exponent
+
+    Notes
+    -----
+    Adapted from
+
+    .. math:: R_m = (1 - q_v) R_a + q_v R_v
+
+    Eq 16, [Romps2017]_ using MetPy-defined constants in place of cited values.
+
+    """
+    return mpconsts.nounit.Rd + specific_humidity * (mpconsts.nounit.Rv - mpconsts.nounit.Rd)
+
+
+@exporter.export
+@preprocess_and_wrap(wrap_like='specific_humidity')
+@process_units(input_dimensionalities={'specific_humidity': 'dimensionless'},
+               output_dimensionalities='[specific_heat_capacity]',
+               output_to='J K**-1 kg**-1 ')
+def moist_air_specific_heat_pressure(specific_humidity):
+    r"""Calculate C_pm, the specific heat at constant pressure for a moist air parcel.
+
+    Parameters
+    ----------
+    specific_humidity : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Specific heat capacity of air at constant pressure
+
+    Examples
+    --------
+    >>> from metpy.calc import moist_air_specific_heat_pressure
+    >>> from metpy.units import units
+    >>> moist_air_specific_heat_pressure(11 * units('g/kg'))
+    <Quantity(1014.07575, 'joule / kelvin / kilogram')>
+
+    See Also
+    --------
+    moist_air_gas_constant, moist_air_poisson_exponent
+
+    Notes
+    -----
+    Adapted from
+
+    .. math:: c_{pm} = (1 - q_v) c_{pa} + q_v c_{pv}
+
+    Eq 17, [Romps2017]_ using MetPy-defined constants in place of cited values.
+
+    """
+    return (mpconsts.nounit.Cp_d
+            + specific_humidity * (mpconsts.nounit.Cp_v - mpconsts.nounit.Cp_d))
+
+
+@exporter.export
+@preprocess_and_wrap(wrap_like='specific_humidity')
+@process_units(
+    input_dimensionalities={'specific_humidity': 'dimensionless'},
+    output_dimensionalities='[dimensionless]'
+)
+def moist_air_poisson_exponent(specific_humidity):
+    r"""Calculate kappa_m, the Poisson exponent for a moist air parcel.
+
+    Parameters
+    ----------
+    specific_humidity : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Poisson exponent of moist air parcel
+
+    Examples
+    --------
+    >>> from metpy.calc import moist_air_poisson_exponent
+    >>> from metpy.units import units
+    >>> moist_air_poisson_exponent(11 * units('g/kg'))
+    <Quantity(0.284955757, 'dimensionless')>
+
+    See Also
+    --------
+    moist_air_gas_constant, moist_air_specific_heat_pressure
+
+    """
+    return (moist_air_gas_constant._nounit(specific_humidity)
+            / moist_air_specific_heat_pressure._nounit(specific_humidity))
+
+
+@exporter.export
+@preprocess_and_wrap(wrap_like='temperature')
+@process_units(input_dimensionalities={'temperature': '[temperature]'},
+               output_dimensionalities='[specific_enthalpy]',
+               output_to='J kg**-1')
+def water_latent_heat_vaporization(temperature):
+    r"""Calculate the latent heat of vaporization for water.
+
+    Accounts for variations in latent heat across valid temperature range.
+
+    Parameters
+    ----------
+    temperature : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Latent heat of vaporization
+
+    Examples
+    --------
+    >>> from metpy.calc import water_latent_heat_vaporization
+    >>> from metpy.units import units
+    >>> water_latent_heat_vaporization(20 * units.degC)
+    <Quantity(2453677.15, 'joule / kilogram')>
+
+    See Also
+    --------
+    water_latent_heat_sublimation, water_latent_heat_melting
+
+    Notes
+    -----
+    Assumption of constant :math:`C_{pv}` limits validity to :math:`0` -- :math:`100^{\circ} C`
+    range.
+
+    .. math:: L = L_0 - (c_{pl} - c_{pv}) (T - T_0)
+
+    Eq 15, [Ambaum2020]_, using MetPy-defined constants in place of cited values.
+
+    """
+    return (mpconsts.nounit.Lv
+            - (mpconsts.nounit.Cp_l - mpconsts.nounit.Cp_v)
+            * (temperature - mpconsts.nounit.T0))
+
+
+@exporter.export
+@preprocess_and_wrap(wrap_like='temperature')
+@process_units(input_dimensionalities={'temperature': '[temperature]'},
+               output_dimensionalities='[specific_enthalpy]',
+               output_to='J kg**-1')
+def water_latent_heat_sublimation(temperature):
+    r"""Calculate the latent heat of sublimation for water.
+
+    Accounts for variations in latent heat across valid temperature range.
+
+    Parameters
+    ----------
+    temperature : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Latent heat of vaporization
+
+    Examples
+    --------
+    >>> from metpy.calc import water_latent_heat_sublimation
+    >>> from metpy.units import units
+    >>> water_latent_heat_sublimation(-15 * units.degC)
+    <Quantity(2837991.13, 'joule / kilogram')>
+
+    See Also
+    --------
+    water_latent_heat_vaporization, water_latent_heat_melting
+
+    Notes
+    -----
+    .. math:: L_s = L_{s0} - (c_{pl} - c_{pv}) (T - T_0)
+
+    Eq 18, [Ambaum2020]_, using MetPy-defined constants in place of cited values.
+
+    """
+    return (mpconsts.nounit.Ls
+            - (mpconsts.nounit.Cp_i - mpconsts.nounit.Cp_v)
+            * (temperature - mpconsts.nounit.T0))
+
+
+@exporter.export
+@preprocess_and_wrap(wrap_like='temperature')
+@process_units(input_dimensionalities={'temperature': '[temperature]'},
+               output_dimensionalities='[specific_enthalpy]',
+               output_to='J kg**-1')
+def water_latent_heat_melting(temperature):
+    r"""Calculate the latent heat of melting for water.
+
+    Accounts for variations in latent heat across valid temperature range.
+
+    Parameters
+    ----------
+    temperature : `pint.Quantity`
+
+    Returns
+    -------
+    `pint.Quantity`
+        Latent heat of vaporization
+
+    Examples
+    --------
+    >>> from metpy.calc import water_latent_heat_melting
+    >>> from metpy.units import units
+    >>> water_latent_heat_melting(-15 * units.degC)
+    <Quantity(365662.294, 'joule / kilogram')>
+
+    See Also
+    --------
+    water_latent_heat_vaporization, water_latent_heat_sublimation
+
+    Notes
+    -----
+    .. math:: L_m = L_{m0} + (c_{pl} - c_{pi}) (T - T_0)
+
+    Body text below Eq 20, [Ambaum2020]_, derived from Eq 15, Eq 18.
+    Uses MetPy-defined constants in place of cited values.
+
+    """
+    return (mpconsts.nounit.Lf
+            - (mpconsts.nounit.Cp_l - mpconsts.nounit.Cp_i)
+            * (temperature - mpconsts.nounit.T0))
+
+
 @exporter.export
 @preprocess_and_wrap(wrap_like='temperature', broadcast=('temperature', 'dewpoint'))
 @check_units('[temperature]', '[temperature]')

src/metpy/constants/__init__.py

@@ -22,20 +22,22 @@
 
 Water
 -----
-======================= ================ ========== ============================ ====================================================
-Name                    Symbol           Short Name Units                        Description
------------------------ ---------------- ---------- ---------------------------- ----------------------------------------------------
-water_molecular_weight  :math:`M_w`      Mw         :math:`\text{g mol}^{-1}`    Molecular weight of water [5]_
-water_gas_constant      :math:`R_v`      Rv         :math:`\text{J (K kg)}^{-1}` Gas constant for water vapor [2]_ [5]_
-density_water           :math:`\rho_l`   rho_l      :math:`\text{kg m}^{-3}`     Maximum recommended density of liquid water, 0-40C [5]_
-wv_specific_heat_press  :math:`C_{pv}`   Cp_v       :math:`\text{J (K kg)}^{-1}` Specific heat at constant pressure for water vapor
-wv_specific_heat_vol    :math:`C_{vv}`   Cv_v       :math:`\text{J (K kg)}^{-1}` Specific heat at constant volume for water vapor
-water_specific_heat     :math:`Cp_l`     Cp_l       :math:`\text{J (K kg)}^{-1}` Specific heat of liquid water at 0C [6]_
-water_heat_vaporization :math:`L_v`      Lv         :math:`\text{J kg}^{-1}`     Latent heat of vaporization for liquid water at 0C [7]_
-water_heat_fusion       :math:`L_f`      Lf         :math:`\text{J kg}^{-1}`     Latent heat of fusion for liquid water at 0C [7]_
-ice_specific_heat       :math:`C_{pi}`   Cp_i       :math:`\text{J (K kg)}^{-1}` Specific heat of ice at 0C [7]_
-density_ice             :math:`\rho_i`   rho_i      :math:`\text{kg m}^{-3}`     Density of ice at 0C
-======================= ================ ========== ============================ ====================================================
+============================== ================ ========== ============================== ==========================================================
+Name                           Symbol           Short Name Units                          Description
+------------------------------ ---------------- ---------- ------------------------------ ----------------------------------------------------------
+water_molecular_weight         :math:`M_w`      Mw         :math:`\text{g mol}^{-1}`      Molecular weight of water [5]_
+water_gas_constant             :math:`R_v`      Rv         :math:`\text{J (K kg)}^{-1}`   Gas constant for water vapor [2]_ [5]_
+density_water                  :math:`\rho_l`   rho_l      :math:`\text{kg m}^{-3}`       Maximum recommended density of liquid water, 0-40C [5]_
+wv_specific_heat_press         :math:`C_{pv}`   Cp_v       :math:`\text{J (K kg)}^{-1}`   Specific heat at constant pressure for water vapor
+wv_specific_heat_vol           :math:`C_{vv}`   Cv_v       :math:`\text{J (K kg)}^{-1}`   Specific heat at constant volume for water vapor
+water_specific_heat            :math:`C_{pl}`   Cp_l       :math:`\text{J (K kg)}^{-1}`   Specific heat of liquid water at 0C [6]_
+water_heat_vaporization        :math:`L_v`      Lv         :math:`\text{J kg}^{-1}`       Latent heat of vaporization for liquid water at 0C [7]_
+water_heat_fusion              :math:`L_f`      Lf         :math:`\text{J kg}^{-1}`       Latent heat of fusion for liquid water at 0C [7]_
+water_heat_sublimation         :math:`L_s`      Ls         :math:`\text{J kg}^{-1}`       Latent heat of sublimation for water, Lv + Lf
+ice_specific_heat              :math:`C_{pi}`   Cp_i       :math:`\text{J (K kg)}^{-1}`   Specific heat of ice at 0C [7]_
+density_ice                    :math:`\rho_i`   rho_i      :math:`\text{kg m}^{-3}`       Density of ice at 0C
+water_triple_point_temperature :math:`T_0`      T0         :math:`\text{K}`               Triple-point temperature of water [2]_
+============================== ================ ========== ============================== ==========================================================
 
 Dry Air
 -------

src/metpy/constants/default.py

@@ -37,9 +37,11 @@
     Cp_l = water_specific_heat = units.Quantity(4.2194, 'kJ / kg / K').to('J / kg / K')
     Lv = water_heat_vaporization = units.Quantity(2.50084e6, 'J / kg')
     Lf = water_heat_fusion = units.Quantity(3.337e5, 'J / kg')
+    Ls = water_heat_sublimation = Lv + Lf
     Cp_i = ice_specific_heat = units.Quantity(2090, 'J / kg / K')
     rho_i = density_ice = units.Quantity(917, 'kg / m^3')
     sat_pressure_0c = units.Quantity(6.112, 'millibar')
+    T0 = water_triple_point_temperature = units.Quantity(273.16, 'K')
 
     # Dry air
     Md = dry_air_molecular_weight = units.Quantity(28.96546e-3, 'kg / mol')

src/metpy/constants/nounit.py

@@ -7,10 +7,17 @@
 from ..units import units
 
 Rd = default.Rd.m_as('m**2 / K / s**2')
+Rv = default.Rv.m_as('m**2 / K / s**2')
 Lv = default.Lv.m_as('m**2 / s**2')
+Lf = default.Lf.m_as('m**2 / s**2')
+Ls = default.Ls.m_as('m**2 / s**2')
 Cp_d = default.Cp_d.m_as('m**2 / K / s**2')
+Cp_l = default.Cp_l.m_as('m**2 / K / s**2')
+Cp_v = default.Cp_v.m_as('m**2 / K / s**2')
+Cp_i = default.Cp_i.m_as('m**2 / K / s**2')
 zero_degc = units.Quantity(0., 'degC').m_as('K')
 sat_pressure_0c = default.sat_pressure_0c.m_as('Pa')
 epsilon = default.epsilon.m_as('')
 kappa = default.kappa.m_as('')
 g = default.g.m_as('m / s**2')
+T0 = default.T0.m_as('K')

src/metpy/units.py

@@ -39,7 +39,9 @@
     '[temperature]': 'K',
     '[dimensionless]': '',
     '[length]': 'm',
-    '[speed]': 'm s**-1'
+    '[speed]': 'm s**-1',
+    '[specific_enthalpy]': 'm**2 s**-2',
+    '[specific_heat_capacity]': 'm**2 s**-2 K-1'
 }
 
 
@@ -83,6 +85,8 @@ def setup_registry(reg):
     reg.define('degrees_east = degree = degrees_E = degreesE = degree_east = degree_E '
                '= degreeE')
     reg.define('dBz = 1e-18 m^3; logbase: 10; logfactor: 10 = dBZ')
+    reg.define('[specific_enthalpy] = [energy] / [mass]')
+    reg.define('[specific_heat_capacity] = [specific_enthalpy] / [temperature]')
 
     # Alias geopotential meters (gpm) to just meters
     reg.define('@alias meter = gpm')