text: """ Commonly used constants in microphysics and aerosol thermodynamics equations as
  well as important model parameters.
  
  ================= ============= ========== ==========        ======================
  Symbol            Variable      Value      Units             Description
  ================= ============= ========== ==========        ======================
  :math:`g`         ``g``         9.8        m s**-2           gravitational constant
  :math:`C_p`       ``Cp``        1004.0     J/kg              specific heat of dry air
                                                               at constant pressure
  :math:`\\rho_w`    ``rho_w``     1000.0     kg m**-3          density of water at STP
  :math:`R_d`       ``Rd``        287.0      J/kg/K            gas constant for dry air
  :math:`R_v`       ``Rv``        461.5      J/kg/K            gas constant for water vapor
  :math:`R`         ``R``         8.314      J/mol/K           universal gas constant
  :math:`M_w`       ``Mw``        0.018      kg/mol            molecular weight of water
  :math:`M_a`       ``Ma``        0.0289     kg/mol            molecular weight of dry air
  :math:`D_v`       ``Dv``        3e-5       m**2/s            diffusivity of water vapor
                                                               in air
  :math:`L_v`       ``L``         2.25e6     J/kg/K            latent heat of vaporization
                                                               of water
  :math:`\\alpha_c`  ``ac``        1.0        unitless          condensation coefficient
  :math:`K_a`       ``Ka``        0.02       J/m/s/K           thermal conductivity of air
  :math:`a_T`       ``at``        0.96       unitless          thermal accommodation
                                                               coefficient
  :math:`\epsilon`  ``epsilon``   0.622      unitless          ratio of :math:`M_w/M_a`
  ================= ============= ========== ==========        ======================
  
  Additionally, a reference table containing the
  `1976 US Standard Atmosphere <http://www.pdas.com/atmos.html>`_ is implemented in the
  constant ``std_atm``, which is a pandas DataFrame with the fields
  
  - ``alt``, altitude in km
  - ``sigma``, ratio of density to sea-level density
  - ``delta``, ratio of pressure to sea-level pressure
  - ``theta``, ratio of temperature to sea-level temperature
  - ``temp``, temperature in K
  - ``press``, pressure in Pa
  - ``dens``, air density in kg/m**3
  - ``k.visc``, air kinematic viscosity
  - ``ratio``, ratio of speed of sound to kinematic viscosity in m**-1
  
  Using default pandas functons, you can interpolate to any reference pressure or
  height level.
  
  """
  import pandas as pd
  from io import StringIO
  import pkg_resources
  from future import standard_library
  standard_library.install_aliases()
  
  g = 9.81             #: Gravitational constant, m/s^2
  Cp = 1004.0          #: Specific heat of dry air at constant pressure, J/kg
  L = 2.25e6           #: Latent heat of condensation, J/kg
  rho_w = 1e3          #: Density of water, kg/m^3
  R = 8.314            #: Universal gas constant, J/(mol K)
  Mw = 18.0/1e3        #: Molecular weight of water, kg/mol
  Ma = 28.9/1e3        #: Molecular weight of dry air, kg/mol
  Rd = R/Ma            #: Gas constant for dry air, J/(kg K)
  Rv = R/Mw            #: Gas constant for water vapor, J/(kg K)
  Dv = 3.e-5           #: Diffusivity of water vapor in air, m^2/s
  ac = 1.0             #: condensation constant
  Ka = 2.e-2           #: Thermal conductivity of air, J/m/s/K
  at = 0.96            #: thermal accomodation coefficient
  epsilon = 0.622      #: molecular weight of water / molecular weight of dry air
  
  # Additional fixed model parameters
  N_STATE_VARS = 7
  STATE_VARS = ['z', 'P', 'T', 'wv', 'wc', 'wi', 'S']
  STATE_VAR_MAP = {var: i for i, var in enumerate(STATE_VARS)}
  
  # Read the standard atmosphere CSV file
  _std_atm_fn = pkg_resources.resource_filename("pyrcel",
                                                "data/std_atm.csv")
  std_atm = pd.read_csv(_std_atm_fn, delim_whitespace=True)
  