psychrometric_vapor_pressure_wet

metpy.calc.psychrometric_vapor_pressure_wet(pressure, dry_bulb_temperature, wet_bulb_temperature, psychrometer_coefficient=None)

Calculate the vapor pressure with wet bulb and dry bulb temperatures.

This uses a psychrometric relationship as outlined in [WMO8], with coefficients from [Fan1987].

Parameters

• pressure (pint.Quantity) – Total atmospheric pressure

• dry_bulb_temperature (pint.Quantity) – Dry bulb temperature

• wet_bulb_temperature (pint.Quantity) – Wet bulb temperature

• psychrometer_coefficient (pint.Quantity, optional) – Psychrometer coefficient. Defaults to 6.21e-4 K^-1.

Returns

pint.Quantity – Vapor pressure

See also

saturation_vapor_pressure

Notes

\[e' = e'_w(T_w) - A p (T - T_w)\]

• \(e'\) is vapor pressure

• \(e'_w(T_w)\) is the saturation vapor pressure with respect to water at temperature \(T_w\)

• \(p\) is the pressure of the wet bulb

• \(T\) is the temperature of the dry bulb

• \(T_w\) is the temperature of the wet bulb

• \(A\) is the psychrometer coefficient

Psychrometer coefficient depends on the specific instrument being used and the ventilation of the instrument.

Changed in version 1.0: Changed signature from (dry_bulb_temperature, wet_bulb_temperature, pressure, psychrometer_coefficient)

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