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Demonstration of evaporative cooling. When the sensor is dipped in ethanol and then taken out to evaporate, the instrument shows progressively lower temperature as the ethanol evaporates. Rain evaporating after falling on hot pavement. Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. [1]
Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid. [ 1 ]
Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss. [6] Humans cannot survive prolonged exposure to a wet-bulb temperature above 35 °C (95 °F). Such a temperature used to be thought not to occur on Earth's surface but has been recorded in some parts of the Indus Valley and Persian Gulf.
Humidity affects the energy budget and thereby influences temperatures in two major ways. First, water vapor in the atmosphere contains "latent" energy. During transpiration or evaporation, this latent heat is removed from surface liquid, cooling the Earth's surface. This is the biggest non-radiative cooling effect at the surface.
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.
In turn, the temperature of the atmosphere drops slightly. [10] In the atmosphere, condensation produces clouds, fog and precipitation (usually only when facilitated by cloud condensation nuclei). The dew point of an air parcel is the temperature to which it must cool before water vapor in the air begins to condense. Condensation in the ...
In technical terms, the dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. [7] At temperatures below the dew point, the rate of condensation will be greater than that of evaporation, forming more liquid water.
The Penman equation describes evaporation (E) from an open water surface, and was developed by Howard Penman in 1948. Penman's equation requires daily mean temperature, wind speed, air pressure, and solar radiation to predict E. Simpler Hydrometeorological equations continue to be used where obtaining such data is impractical, to give comparable results within specific contexts, e.g. humid vs ...