# Dew Point

The dew point is the temperature below which the water vapor in a volume of humid air at a constant barometric pressure will condense into liquid water. Condensed water is called dew when it forms on a solid surface.

The dew point is a water-to-air saturation temperature. The dew point is associated with relative humidity. A high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the dew point remains constant and temperature increases, relative humidity decreases.

General aviation pilots use dew-point data to calculate the likelihood of carburetor icing and fog, and to estimate the height of the cloud base.

At a given temperature but independent of barometric pressure, the dew point is a consequence of the absolute humidity, the mass of water per unit volume of air. If both the temperature and pressure rise, however, the dew point will rise and the relative humidity will lower accordingly. Reducing the absolute humidity without changing other variables will bring the dew point back down to its initial value. In the same way, increasing the absolute humidity after a temperature drop brings the dew point back down to its initial level. If the temperature rises in conditions of constant pressure, then the dew point will remain constant but the relative humidity will drop. For this reason, a constant relative humidity (%) with different temperatures implies that when it's hotter, a higher fraction of the air is water vapor than when it's cooler.

At a given barometric pressure but independent of temperature, the dew point indicates the mole fraction of water vapor in the air, or, put differently, determines the specific humidity of the air. If the pressure rises without changing this mole fraction, the dew point will rise accordingly; Reducing the mole fraction, i.e., making the air less humid, would bring the dew point back down to its initial value. In the same way, increasing the mole fraction after a pressure drop brings the relative humidity back up to its initial level. Considering New York (33 ft elevation) and Denver (5,280 ft elevation), for example, this means that if the dew point and temperature in both cities are the same, then the mass of water vapor per cubic meter of air will be the same, but the mole fraction of water vapor in the air will be greater in Denver.

### Other articles related to "dew point, point, dew":

Air Dryer - Desiccant Dryer
... The duty of the desiccant is to bring the pressure dew point of the compressed air to a level in which the water will no longer condense, or to remove as ... A standard dew point that is expected by a regenerative dryer is −40 °C (−40 °F), this means that when the air leaves the dryer there is as much water in the air as if the air had ... Required dew point is dependant on application and −70 °C is required in some applications ...
Dew Point - Frost Point
... The frost point is similar to the dew point, in that it is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to be ... Compare with sublimation.) The frost point for a given parcel of air is always higher than the dew point, as the stronger bonding between water molecules on the surface of ice ...
Dew Point Depression
... The dew point depression (T-Td) is the difference between the temperature and dew point temperature at a certain height in the atmosphere ... the lower troposphere, more moisture (small dew point depression) results in lower cloud bases and is also important to severe thunderstorms ... increased when there is a mid-level dry layer (large dew point depression) known as a "dry punch", which is favorable for convection if the lower layer is buoyant ...
Surface Weather Observation - Data Reported
... Dew Point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water ... The condensed water is called dew ... The dew point is a saturation point ...
Precipitation (meteorology) - How The Air Becomes Saturated - Cooling Air To Its Dew Point
... The dew point is the temperature to which a parcel must be cooled in order to become saturated, and (unless super-saturation occurs) condenses to water ... There are four main mechanisms for cooling the air to its dew point adiabatic cooling, conductive cooling, radiational cooling, and evaporative cooling ...

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