psychrometric_vapor_pressure_wet¶

metpy.calc.psychrometric_vapor_pressure_wet(dry_bulb_temperature, wet_bulb_temperature, pressure, psychrometer_coefficient=<Quantity(0.000621, '1 / kelvin')>)[source]¶

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

This uses a psychrometric relationship as outlined in [WMO8-2014], with coefficients from [Fan1987].

Parameters

dry_bulb_temperature (pint.Quantity) – Dry bulb temperature
wet_bulb_temperature (pint.Quantity) – Wet bulb temperature
pressure (pint.Quantity) – Total atmospheric pressure
psychrometer_coefficient (pint.Quantity, optional) – Psychrometer coefficient. Defaults to 6.21e-4 K^-1.

Returns

pint.Quantity – 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.