hum_subs.py

import numpy as np
import sys
from util_subs import (CtoK)

def VaporPressure(temp, P, phase, meth):
    """
    Calculate the saturation vapor pressure

    For temperatures above 0 deg C the vapor pressure over liquid water
    is calculated.

    The optional parameter 'liquid' changes the calculation to vapor pressure
    over liquid water over the entire temperature range.

    The current default fomulas are Hyland and Wexler for liquid and
    Goff Gratch for ice.

    Parameters
    ----------
    temp : float
        Temperature in [deg C]
    phase : str
        'liquid' : Calculate vapor pressure over liqiud water or
        'ice' : Calculate vapor pressure over ice
    meth : str
        formula to be used
        MartiMauersberger   : vaporpressure formula from Marti Mauersberger
        MagnusTetens        : vaporpressure formula from Magnus Tetens
        GoffGratch          : vaporpressure formula from Goff Gratch
        Buck_original       : vaporpressure formula from Buck (original)
        Buck_manual         : vaporpressure formula from the Buck manual
        CIMO                : vaporpressure formula recommended by CIMO
        Vaisala             : vaporpressure formula from Vaisala
        WMO_Goff            : vaporpressure formula from WMO, which should have been Goff
        WMO2000             : vaporpressure formula from WMO (2000) containing a typo
        Wexler              : vaporpressure formula from Wexler (1976)
        Sonntag             : vaporpressure formula from Sonntag (1994)
        Bolton              : vaporpressure formula from Bolton (1980)
        Fukuta              : vaporpressure formula from Fukuta (2003)
        HylandWexler        : vaporpressure formula from Hyland and Wexler (1983)
        IAPWS               : vaporpressure formula from IAPWS (2002)
        Preining            : vaporpressure formula from Preining (2002)
        MurphyKoop          : vaporpressure formula from Murphy and Koop (2005)

    Returns
    -------
    P : float
        Saturation vapor pressure in [hPa]


    Author
    ------
    Ported to Python and modified by S. Biri from Holger Voemel's original
    """

    Psat = np.zeros(temp.size)*np.nan
    if (np.nanmin(temp) > 200):  # if Ta in Kelvin convert to Celsius
        temp = temp-273.16
    T = np.copy(temp)+273.16    #  Most formulas use T in [K]
                                #  Formulas using [C] use the variable temp
    #  Calculate saturation pressure over liquid water
    if (phase == 'liquid'):
        if (meth == 'HylandWexler' or meth == ''):
            """
            Source Hyland, R. W. and A. Wexler, Formulations for the
            Thermodynamic Properties of the saturated Phases of H2O from
            173.15K to 473.15K, ASHRAE Trans, 89(2A), 500-519, 1983."""
            Psat = np.exp(-0.58002206e4/T+0.13914993e1-0.48640239e-1*T +
                          0.41764768e-4*np.power(T, 2) -
                          0.14452093e-7*np.power(T, 3) +
                          0.65459673e1*np.log(T))/100
        if (meth == 'Hardy'):
            """
            Source Hardy, B., 1998, ITS-90 Formulations for Vapor Pressure,
            Frostpoint Temperature, Dewpoint Temperature, and Enhancement
            Factors in the Range -100 to +100°C, The Proceedings of the Third
            International Symposium on Humidity & Moisture, London, England"""
            Psat = np.exp(-2.8365744e3/np.power(T, 2)-6.028076559e3/T +
                          1.954263612e1-2.737830188e-2*T +
                          1.6261698e-5*np.power(T, 2) +
                          7.0229056e-10*np.power(T, 3) -
                          1.8680009e-13*np.power(T, 4) +
                          2.7150305*np.log(T))/100
        if (meth == 'Preining'):
            """Source : Vehkamaeki, H., M. Kulmala, I. Napari, K. E. J.
            Lehtinen, C.Timmreck, M. Noppel, and A. Laaksonen (2002),
            J. Geophys. Res., 107, doi:10.1029/2002JD002184."""
            Psat = np.exp(-7235.424651/T+77.34491296+5.7113e-3*T -
                          8.2*np.log(T))/100
        if (meth == 'Wexler'):
            """Wexler, A., Vapor Pressure Formulation for Water in Range 0 to
            100 C. A Revision, Journal of Research of the National Bureau of
            Standards - A. Physics and Chemistry, September - December 1976,
            Vol. 80A, Nos.5 and 6, 775-785"""
            Psat = np.exp(-0.29912729e4*np.power(T, -2) -
                          0.60170128e4*np.power(T, -1) +
                          0.1887643854e2-0.28354721e-1*T +
                          0.17838301e-4*np.power(T, 2) -
                          0.84150417e-9*np.power(T, 3) +
                          0.44412543e-12*np.power(T, 4) +  # This line was corrected from '-' to '+' following the original citation. (HV 20140819). The change makes only negligible difference
                          2.858487*np.log(T))/100
        if ((meth == 'GoffGratch') or (meth == 'MartiMauersberger')):
            """Marti and Mauersberger don't have a vapor pressure curve over
            liquid. Using Goff Gratch instead; Goff Gratch formulation Source :
            Smithsonian Meteorological Tables, 5th edition, p. 350, 1984
            From original source: Goff & Gratch (1946), p. 107)
            """
            Ts = 373.16  # steam point temperature in K
            ews = 1013.246  # saturation pressure at steam point temperature
            Psat = np.power(10, -7.90298*(Ts/T-1)+5.02808*np.log10(Ts/T) -
                            1.3816e-7*(np.power(10, 11.344*(1-T/Ts))-1) +
                            8.1328e-3*(np.power(10, -3.49149*(Ts/T-1))-1) +
                            np.log10(ews))
        if (meth == 'CIMO'):
            """Source: Annex 4B, Guide to Meteorological Instruments and
            Methods of Observation, WMO Publication No 8, 7th edition, Geneva,
            2008. (CIMO Guide)"""
            Psat = (6.112*np.exp(17.62*temp/(243.12+temp)) *
                    (1.0016+3.15e-6*P-0.074/P))
        if (meth == 'MagnusTetens'):
            """Source: Murray, F. W., On the computation of \
                         saturation vapor pressure, J. Appl. Meteorol., \
                         6, 203-204, 1967."""
            Psat = np.power(10, 7.5*(temp)/(temp+237.5)+0.7858)
            # Murray quotes this as the original formula and
            Psat = 6.1078*np.exp(17.269388*temp/(temp+237.3))
            # this as the mathematical aquivalent in the form of base e.
        if (meth == 'Buck'):
            """Bucks vapor pressure formulation based on Tetens formula.
            Source: Buck, A. L., New equations for computing vapor pressure and
            enhancement factor, J. Appl. Meteorol., 20, 1527-1532, 1981."""
            Psat = (6.1121*np.exp(17.502*temp/(240.97+temp)) *
                    (1.0007+(3.46e-6*P)))
        if (meth == 'Buck2'):
            """Bucks vapor pressure formulation based on Tetens formula.
            Source: Buck Research, Model CR-1A Hygrometer Operating Manual,
            Sep 2001"""
            Psat = (6.1121*np.exp((18.678-(temp)/234.5)*(temp)/(257.14+temp)) *
                    (1+1e-4*(7.2+P*(0.0320)+5.9e-6*np.power(T, 2))))
        if (meth == 'WMO'):
            """Intended WMO formulation, originally published by Goff (1957)
            incorrectly referenced by WMO technical regulations, WMO-NO 49,
            Vol I, General Meteorological Standards and Recommended Practices,
            App. A, Corrigendum Aug 2000. and incorrectly referenced by WMO
            technical regulations, WMO-NO 49, Vol I, General Meteorological
            Standards and Recommended Practices, App. A, 1988."""
            Ts = 273.16  # triple point temperature in K
            Psat = np.power(10, 10.79574*(1-Ts/T)-5.028*np.log10(T/Ts) +
                            1.50475e-4*(1-np.power(10, -8.2969*(T/Ts-1))) +
                            0.42873e-3*(np.power(10, -4.76955*(1-Ts/T))-1) +
                            0.78614)
        if (meth == 'WMO2000'):
            """WMO formulation, which is very similar to Goff & Gratch.
            Source : WMO technical regulations, WMO-NO 49, Vol I, General
            Meteorological Standards and Recommended Practices, App. A,
            Corrigendum Aug 2000."""
            Ts = 273.16  # triple point temperature in K
            Psat = np.power(10, 10.79574*(1-Ts/T)-5.028*np.log10(T/Ts) +
                            1.50475e-4*(1-np.power(10, -8.2969*(T/Ts-1))) +
                            0.42873e-3*(np.power(10, -4.76955*(1.-Ts/T))-1) +
                            0.78614)
        if (meth == 'Sonntag'):
            """Source: Sonntag, D., Advancements in the field of hygrometry,
            Meteorol. Z., N. F., 3, 51-66, 1994."""
            Psat = np.exp(-6096.9385*np.power(T, -1)+16.635794 -
                          2.711193e-2*T+1.673952e-5*np.power(T, 2) +
                          2.433502*np.log(T))#*(1.0016+P*3.15e-6-0.074/P)
        if (meth == 'Bolton'):
            """Source: Bolton, D., The computation of equivalent potential
            temperature, Monthly Weather Report, 108, 1046-1053, 1980.
            equation (10)"""
            Psat = 6.112*np.exp(17.67*temp/(temp+243.5))
        if (meth == 'IAPWS'):
            """Source: Wagner W. and A. Pruss (2002), The IAPWS formulation
            1995 for the thermodynamic properties of ordinary water substance
            for general and scientific use, J. Phys. Chem. Ref. Data, 31(2),
            387-535. This is the 'official' formulation from the International
            Association for the Properties of  Water and Steam The valid range
            of this formulation is 273.16 <= T <= 647.096 K and is based on the
            ITS90 temperature scale."""
            Tc = 647.096   # K   : Temperature at the critical point
            Pc = 22.064e4  #  hPa : Vapor pressure at the critical point
            nu = (1-T/Tc)
            a1, a2, a3 = -7.85951783, 1.84408259, -11.7866497
            a4, a5, a6 = 22.6807411, -15.9618719, 1.80122502
            Psat = (Pc*np.exp(Tc/T*(a1*nu+a2*np.power(nu, 1.5) +
                    a3*np.power(nu, 3)+a4*np.power(nu, 3.5) +
                    a5*np.power(nu, 4)+ a6*np.power(nu, 7.5))))
        if (meth == 'MurphyKoop'):
            """Source : Murphy and Koop, Review of the vapour pressure of ice
            and supercooled water for atmospheric applications, Q. J. R.
            Meteorol. Soc (2005), 131, pp. 1539-1565."""
            Psat = np.exp(54.842763-6763.22/T-4.210*np.log(T)+0.000367*T +
                          np.tanh(0.0415*(T-218.8))*(53.878-1331.22/T -
                          9.44523*np.log(T)+0.014025*T))/100
    # Calculate saturation pressure over ice ----------------------------------
    elif (phase == 'ice'):
        """Default uses Goff Gratch over ice. There is little ambiguity in the
        ice saturation curve. Goff Gratch is widely used."""
        if (meth == 'MartiMauersberger'):
            """Source : Marti, J. and K Mauersberger, A survey and new
            measurements of ice vapor pressure at temperatures between 170 and
            250 K, GRL 20, 363-366, 1993."""
            Psat = np.power(10, -2663.5/T+12.537)/100
        if (meth == 'HylandWexler'):
            """Source Hyland, R. W. and A. Wexler, Formulations for the
            Thermodynamic Properties of the saturated Phases of H2O from
            173.15K to 473.15K, ASHRAE Trans, 89(2A), 500-519, 1983."""
            Psat = np.exp(-0.56745359e4/T+0.63925247e1-0.96778430e-2*T +
                          0.62215701e-6*np.power(T, 2) +
                          0.20747825e-8*np.power(T, 3) -
                          0.9484024e-12*np.power(T, 4) +
                          0.41635019e1*np.log(T))/100
        if (meth == 'Wexler'):
            """Wexler, A., Vapor pressure formulation for ice, Journal of
            Research of the National Bureau of Standards-A. 81A, 5-20, 1977."""
            Psat = np.exp(-0.58653696e4*np.power(T, -1)+0.22241033e2 +
                          0.13749042e-1*T-0.34031775e-4*np.power(T, 2) +
                          0.26967687e-7*np.power(T, 3) +
                          0.6918651*np.log(T))/100
        if (meth == 'Hardy'):
            """Source Hardy, B., 1998, ITS-90 Formulations for Vapor Pressure,
            Frostpoint Temperature, Dewpoint Temperature, and Enhancement
            Factors in the Range -100 to +100°C, The Proceedings of the Third
            International Symposium on Humidity & Moisture, London, England.
            These coefficients are updated to ITS90 based on the work by
            Bob Hardy at Thunder Scientific: http://www.thunderscientific.com/
            tech_info/reflibrary/its90formulas.pdf """
            Psat = np.exp(-0.58666426e4*np.power(T, -1)+0.2232870244e2 +
                          0.139387003e-1*T-0.34262402e-4*np.power(T, 2) +
                          0.27040955e-7*np.power(T, 3) +
                          0.67063522e-1*np.log(T))/100
        if (meth == 'GoffGratch' or meth == '' or meth == 'IAPWS'):
            """IAPWS does not provide a vapor pressure formulation over ice use
            Goff Gratch instead.
            Source : Smithsonian Meteorological Tables, 5th edition, p. 350,
            1984"""
            ei0 = 6.1071  # mbar
            T0 = 273.16   # triple point in K
            Psat = np.power(10, -9.09718*(T0/T-1)-3.56654*np.log10(T0/T) +
                            0.876793*(1-T/T0)+np.log10(ei0))
        if (meth == 'MagnusTetens'):
            """Source: Murray, F. W., On the computation of saturation vapor
            pressure, J. Appl. Meteorol., 6, 203-204, 1967."""
            Psat = np.power(10, 9.5*temp/(265.5+temp)+0.7858)
            #  Murray quotes this as the original formula and
            Psat = 6.1078*np.exp(21.8745584*(T-273.16)/(T-7.66))
            # this as the mathematical aquivalent in the form of base e.
        if (meth == 'Buck'):
            """Bucks vapor pressure formulation based on Tetens formula.
            Source: Buck, A. L., New equations for computing vapor pressure and
            enhancement factor, J. Appl. Meteorol., 20, 1527-1532, 1981."""
            Psat = (6.1115*np.exp(22.452*temp/(272.55+temp)) *
                    (1.0003+(4.18e-6*P)))
        if (meth == 'Buck2'):
            """Bucks vapor pressure formulation based on Tetens formula.
            Source: Buck Research, Model CR-1A Hygrometer Operating Manual,
            Sep 2001"""
            Psat = (6.1115*np.exp((23.036-temp/333.7)*temp/(279.82+temp)) *
                    (1+1e-4*(2.2+P*(0.0383+6.4e-6*np.power(T, 2)))))
        if (meth == 'CIMO'):
            """Source: Annex 4B, Guide to Meteorological Instruments and
            Methods of Observation, WMO Publication No 8, 7th edition, Geneva,
            2008. (CIMO Guide)"""
            Psat = (6.112*np.exp(22.46*temp/(272.62+temp)) *
                    (1.0016+3.15e-6*P-0.074/P))
        if (meth == 'WMO' or meth == 'WMO2000'):
            """There is no typo issue in the WMO formulations for ice.
            WMO formulation, which is very similar to Goff & Gratch.
            Source : WMO technical regulations, WMO-NO 49, Vol I, General
            Meteorological Standards and Recommended Practices, Aug 2000,
            App. A."""
            T0 = 273.16  # triple point temperature in K
            Psat = np.power(10, -9.09685*(T0/T-1)-3.56654*np.log10(T0/T) +
                            0.87682*(1-T/T0)+0.78614)
        if (meth == 'Sonntag'):
            """Source: Sonntag, D., Advancements in the field of hygrometry,
            Meteorol. Z., N. F., 3, 51-66, 1994."""
            Psat = np.exp(-6024.5282*np.power(T, -1)+24.721994+1.0613868e-2*T -
                          1.3198825e-5*np.power(T, 2)-0.49382577*np.log(T))
        if (meth == 'MurphyKoop'):
            """Source : Murphy and Koop, Review of the vapour pressure of ice
            and supercooled water for atmospheric applications, Q. J. R.
            Meteorol. Soc (2005), 131, pp. 1539-1565."""
            Psat = np.exp(9.550426-5723.265/T+3.53068*np.log(T) -
                          0.00728332*T)/100

        s = np.where(temp > 0)
        if (s.size[0] >= 1):
            """Independent of the formula used for ice, use Hyland Wexler
            (water) for temperatures above freezing (see above).
            Source Hyland, R. W. and A. Wexler, Formulations for the
            Thermodynamic Properties of the saturated Phases of H2O from
            173.15K to 473.15K, ASHRAE Trans, 89(2A), 500-519, 1983."""
            Psat_w = np.exp(-0.58002206e4/T+0.13914993e1-0.48640239e-1*T +
                            0.41764768e-4*np.power(T, 2) -
                            0.14452093e-7*np.power(T, 3) +
                            0.65459673e1*np.log(T))/100
            Psat[s] = Psat_w[s]

    return Psat
#-----------------------------------------------------------------------------


def qsat_sea(T, P, qmeth):
    """ Computes surface saturation specific humidity (g/kg)

    Parameters
    ----------
    T : float
        temperature ($^\\circ$\\,C)
    P : float
        pressure (mb)
    qmeth : str
        method to calculate vapor pressure

    Returns
    -------
    qs : float
    """
    T = np.asarray(T)
    if (np.nanmin(T) > 200):  # if Ta in Kelvin convert to Celsius
        T = T-CtoK
    ex = VaporPressure(T, P, 'liquid', qmeth)
    es = 0.98*ex  # reduction at sea surface
    qs = 622*es/(P-0.378*es)
    return qs
#-----------------------------------------------------------------------------


def qsat_air(T, P, rh, qmeth):
    """ Computes saturation specific humidity (g/kg) as in C35

    Parameters
    ----------
    T : float
        temperature ($^\circ$\,C)
    P : float
        pressure (mb)
    rh : float
       relative humidity (%)
    qmeth : str
        method to calculate vapor pressure

    Returns
    -------
    q : float
    em : float
    """
    T = np.asarray(T)
    if (np.nanmin(T) > 200):  # if Ta in Kelvin convert to Celsius
        T = T-CtoK
    es = VaporPressure(T, P, 'liquid', qmeth)
    em = 0.01*rh*es
    q = 622*em/(P-0.378*em)
    return q
#------------------------------------------------------------------------------


def get_hum(hum, T, sst, P, qmeth):
    """
    Get specific humidity output

    Parameters
    ----------
    hum : array
        humidity input switch 2x1 [x, values] default is relative humidity
            x='rh' : relative humidity in %
            x='q' : specific humidity (g/kg)
            x='Td' : dew point temperature (K)
    T : float
        air temperature in K
    sst : float
        sea surface temperature in K
    P : float
        air pressure at sea level in hPa
    qmeth : str
        method to calculate specific humidity from vapor pressure

    Returns
    -------
    qair : float
        specific humidity of air
    qsea : float
        specific humidity over sea surface

    """
    if (hum == None):
        RH = np.ones(sst.shape)*80
        qsea = qsat_sea(sst, P, qmeth)/1000     # surface water q (g/kg)
        qair = qsat_air(T, P, RH, qmeth)/1000   # q of air (g/kg)
    elif (hum[0] not in ['rh', 'q', 'Td']):
        sys.exit("unknown humidity input")
        qair, qsea = np.nan, np.nan
    elif (hum[0] == 'rh'):
        RH = hum[1]
        if (np.all(RH < 1)):
            sys.exit("input relative humidity units should be \%")
            qair, qsea = np.nan, np.nan
        qsea = qsat_sea(sst, P, qmeth)/1000    # surface water q (g/kg)
        qair = qsat_air(T, P, RH, qmeth)/1000  # q of air (g/kg)
    elif (hum[0] == 'q'):
        qair = hum[1]
        qsea = qsat_sea(sst, P, qmeth)/1000  # surface water q (g/kg)
    elif (hum[0] == 'Td'):
        Td = hum[1] # dew point temperature (K)
        Td = np.where(Td < 200, np.copy(Td)+CtoK, np.copy(Td))
        T = np.where(T < 200, np.copy(T)+CtoK, np.copy(T))
        esd = 611.21*np.exp(17.502*((Td-273.16)/(Td-32.19)))
        es = 611.21*np.exp(17.502*((T-273.16)/(T-32.19)))
        RH = 100*esd/es
        qair = qsat_air(T, P, RH, qmeth)/1000  # q of air (g/kg)
        qsea = qsat_sea(sst, P, qmeth)/1000    # surface water q (g/kg)
    return qair, qsea
#------------------------------------------------------------------------------