earthkit.meteo.thermo.xarray.ept_from_dewpoint

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

Compute the equivalent potential temperature from dewpoint.

Parameters:

• t (xarray.DataArray) – Temperature (K)

• td (xarray.DataArray) – Dewpoint (K)

• p (xarray.DataArray) – Pressure (Pa)

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

Returns:

Equivalent potential temperature (K)

Return type:

xarray.DataArray

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:

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

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

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

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

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

• “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)