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At 100% relative humidity, air is saturated and at its dew point: the water vapor pressure would permit neither evaporation of nearby liquid water nor condensation to grow the nearby water; neither sublimation of nearby ice nor deposition to grow the nearby ice. Relative humidity can exceed 100%, in which case the air is supersaturated. Cloud ...
If all the other factors influencing humidity remain constant, at ground level the relative humidity rises as the temperature falls; this is because less vapor is needed to saturate the air. In normal conditions, the dew point temperature will not be greater than the air temperature, since relative humidity typically [5] does not exceed 100%. [6]
Relationship to relative humidity: The relative humidity (RH) of air in equilibrium with a sample is also called the Equilibrium Relative Humidity (ERH) and is usually given as a percentage. [1] It is equal to water activity according to E R H = a w × 100 % . {\displaystyle \mathrm {ERH} =a_{w}\times 100\%.}
For a constant temperature, the smaller the difference, the more moisture there is, and the higher the relative humidity. In the lower troposphere, more moisture (small dew point depression) results in lower cloud bases and lifted condensation levels (LCL). LCL height is an important factor modulating severe thunderstorms.
The wet-bulb temperature is the lowest temperature that may be achieved by evaporative cooling of a water-wetted, ventilated surface.. By contrast, the dew point is the temperature to which the ambient air must be cooled to reach 100% relative humidity assuming there is no further evaporation into the air; it is the temperature where condensation (dew) and clouds would form.
Relative humidity is defined relative to saturation vapor pressure. [18] Equilibrium vapor pressure does not require the condensed phase to be a flat surface; it might consist of tiny droplets possibly containing solutes (impurities), such as a cloud.
The saturation vapor pressure of water at any given temperature is the vapor pressure when relative humidity is 100%. One formula is Tetens' equation from [15] used to find the saturation vapor pressure is: = (()) where: , saturation vapor pressure (kPa), temperature
The measurements are usually expressed as specific humidity or percent relative humidity. The temperatures of the atmosphere and the water surface determine the equilibrium vapor pressure; 100% relative humidity occurs when the partial pressure of water vapor is equal to the equilibrium vapor pressure.