"""Utility module."""
import datetime
import sys
import typing as t
import numpy as np
import pint
import xarray as xr
from ..constants import MM, K
if sys.version_info >= (3, 11):
def _utcnow():
return datetime.datetime.now(datetime.UTC)
else:
def _utcnow():
return datetime.datetime.utcnow()
[docs]
def utcnow(isoformat: bool = True):
result = _utcnow()
if isoformat:
return result.replace(microsecond=0).isoformat()
else:
return result
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def number_density(p: pint.Quantity, t: pint.Quantity) -> pint.Quantity:
"""Compute air number density from air pressure and air temperature.
Args:
p: Air pressure.
t: Air temperature.
Returns:
Number density.
Notes:
The air number density is computed according to the ideal gas law:
.. math::
n = \\frac{p}{k_B T}
where :math:`p` is the air pressure, :math:`k_B` is the Boltzmann constant,
and :math:`T` is the air temperature.
"""
return (p / (K * t)).to_base_units()
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def molar_mass(molecules: t.List[str]) -> xr.DataArray:
return xr.DataArray(
data=np.array([MM[m] for m in molecules]),
coords={"m": ("m", molecules)},
attrs={
"long_name": "molar mass",
"standard_name": "molar_mass",
"units": "g/mol",
},
)
[docs]
def air_molar_mass_from_mass_fraction(y: xr.DataArray) -> xr.DataArray:
r"""
Compute the air molar mass from the of air constituents mass fractions.
Args:
y: Mass fraction as a function of molecule (`m`) and altitude (`z`).
Returns:
Air molar mass as a function of altitude (`z`).
Notes:
The air molar mass is computed according to the following equation:
.. math::
m_{\mathrm{air}} (z) = \left(
\sum_{\mathrm{M}} \frac{
y_{\mathrm{M}} (z)
}{
m_{\mathrm{M}}
}
\right)^{-1}
where:
* :math:`y_{\mathrm{M}} (z)` is the mass fraction of molecule M at altitude
:math:`z`,
* :math:`m_{\mathrm{M}}` is the molar mass of molecule M.
"""
# compute molar masses along molecular species
molecules = y.m.values
mm = xr.DataArray(
data=[MM[m] for m in molecules],
coords={"m": ("m", molecules)},
)
# compute air molar mass
mm_inv = 1 / mm
weighted_mean_mm_inv = (mm_inv * y).sum(dim="m") / y.sum(dim="m")
mm_air = 1 / weighted_mean_mm_inv
mm_air.attrs.update({"units": "g/mol"})
return mm_air
Joseki