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In hot summer weather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the heat index, a relative humidity of 75% at air temperature of 80.0 °F (26.7 °C) would feel like 83.6 ± 1.3 °F (28.7 ± 0.7 °C). [13] [14]
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to produce a relative humidity of 100%. [1] This temperature depends on the pressure and water content of the air.
The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. For example, when the temperature is 32 °C (90 °F) with 70% relative humidity, the heat index is 41 °C (106 °F ...
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:
When the two tendencies are in balance— and the air and food are stable—the air's relative humidity (expressed as a fraction instead of as a percentage) is taken to be the water activity, a w. Thus, water activity is the thermodynamic activity of water as solvent and the relative humidity of the surrounding air at equilibrium.
Schematic of the LCL in relation to the temperature (T) and dew point and their altitude (Z); the moist adiabatic temperature curve above the LCL is also sketched for reference The lifting condensation level or lifted condensation level ( LCL ) is the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to ...
Atmospheric thermodynamics is the study of heat-to-work transformations (and their reverse) that take place in the Earth's atmosphere and manifest as weather or climate. . Atmospheric thermodynamics use the laws of classical thermodynamics, to describe and explain such phenomena as the properties of moist air, the formation of clouds, atmospheric convection, boundary layer meteorology, and ...
T a is dry-bulb temperature (°C) RH is relative humidity (%) exp represents the exponential function; The Australian formula includes the important factor of humidity and is somewhat more involved than the simpler North American wind chill model. The North American formula was designed to be applied at low temperatures (as low as −46 °C or ...