earthkit.meteo.thermo.ept_from_dewpoint

earthkit.meteo.thermo.ept_from_dewpoint(t: ArrayLike, td: ArrayLike, p: ArrayLike, method: str = 'ifs') → ArrayLike

earthkit.meteo.thermo.ept_from_dewpoint(t: xarray.DataArray, td: xarray.DataArray, p: xarray.DataArray, method: str = 'ifs') → xarray.DataArray

earthkit.meteo.thermo.ept_from_dewpoint(t: earthkit.data.FieldList, td: earthkit.data.FieldList, p: earthkit.data.FieldList, method: str = 'ifs') → earthkit.data.FieldList

Compute the equivalent potential temperature from dewpoint.

Parameters:

• t (number or array-like) – Temperature (K)

• td (number or array-like) – Dewpoint (K)

• p (number or array-like) – Pressure (Pa)

• method (str, optional) – Specify the computation method. The possible values are: “ifs”, “bolton35”, “bolton39”, “bolton43”.

Returns:

Equivalent potential temperature (K)

Return type:

number or array-like

The actual computation is based on the value of method:

• “ifs”: the formula from the IFS model [IFS-CY47R3-PhysicalProcesses] (Chapter 6.11) is used:

  \[\Theta_{e} = \Theta \operatorname{exp}(\frac{L_{v} q}{c_{pd} t_{LCL}})\]

• “bolton35”: Eq (35) from [Bolton1980] is used:

  \[\Theta_{e} = \Theta (\frac{10^{5}}{p})^{\kappa 0.28 w} \operatorname{exp}(\frac{2675 w}{t_{LCL}})\]

• “bolton39”: Eq (39) from [Bolton1980] is used:

  \[\Theta_{e} = t (\frac{10^{5}}{p-e})^{\kappa} (\frac{t}{t_{LCL}})^{0.28 w} \operatorname{exp}[(\frac{3036}{t_{LCL}} - 1.78)w(1+0.448 w)]\]

• “bolton43”: Eq (43) from [Bolton1980] is used:

  \[\Theta_{e} = t (\frac{10^{5}}{p})^{\kappa (1-0.28\; 10^{-3}w)} exp[(\frac{3376}{t_{LCL}} - 2.54)w(1+0.81w)]\]

where:

• \(\Theta\) is the potential_temperature()

• \(t_{LCL}\) is the temperature at the Lifting Condensation Level computed with lcl_temperature() using option:

  • method=”davis” when method is “ifs”

  • method=”bolton” when method is “bolton35”, “bolton39”, or “bolton43”

• \(q\) is the specific humidity computed with specific_humidity_from_dewpoint()

• \(w\): is the mixing ratio computed with mixing_ratio_from_dewpoint()

• \(e\) is the vapour pressure computed with vapour_pressure_from_mixing_ratio()

• \(L_{v}\): is the latent heat of vaporisation (see earthkit.meteo.constants.Lv)

• \(c_{pd}\) is the specific heat of dry air on constant pressure (see earthkit.meteo.constants.c_pd)

• \(\kappa = R_{d}/c_{pd}\) (see earthkit.meteo.constants.kappa)

Implementations

ept_from_dewpoint() calls one of the following implementations depending on the type of the input arguments:

• earthkit.meteo.thermo.array.ept_from_dewpoint() for array-like

• earthkit.meteo.thermo.xarray.ept_from_dewpoint() for xarray.DataArray

• earthkit.meteo.thermo.fieldlist.ept_from_dewpoint() for FieldList

The function returns an object of the same type as the input arguments.