movement of water between Earth and the atmosphere
the process whereby molecules break free of the liquid volume (opposite of condensation)
the process whereby water vapor molecules randomly collide with the water surface and bond with adjacent molecules. (opposite of evaporation)
saturation is the equilibrium resulting from the constant gains and losses of evaporation and condensation.
the change of phase between ice and water vapor, without passing through the liquid phase (opposite of deposition)
the change of phase between water vapor and ice, without passing through the liquid phase (opposite of sublimation)
the amount of water vapor in the air
part of the total atmospheric pressure due to water vapor
saturation vapor pressure
Because there is a maximum amount of water vapor that can exist, there is a corresponding maximum amount of vapor pressure that can exist called saturation vapor pressure.
the density of water vapor, expressed as the number of grams of water vapor contained in a cubic meter of air.
an index for representing atmospheric moisture
saturation specific humidity
Because there is a maximum amount of water vapor that can exist at a particular temperature, there is a corresponding maximum specific humidity.
the measure of the mass of water vapor relative to the mass of the other gases of the atmosphere
saturation mixing ratio
the maximum possible mixing ratio
relative humidity (RH)
The amount of water vapor in the air to the maximum possible at the current temperature.
dew point temperature (dew point)
the temperature at which saturation occurs.
when the temperature at which saturation occurs is below 0 degrees C (32 degrees F), we refer to it as the frost point (as opposed to the dew point)
a type of fog that develops when falling raindrops evaporate enough water vapor into the air to saturate it.
fog that forms when cold air moves over a warmer water surface
[seldom if ever happens because heterogeneous nucleation happens instead] droplets form by the chance collision and bonding of water vapor molecules under supersaturated conditions.
[often happens] the formation of water droplets onto hygroscopic partices (condensation nuclei/certain aerosols)... these particles then dissolve into the water to form a solution.
the hygroscopic particles (certain water-attracting aerosols) on which water droplets form during the process of heterogeneous nucleation.
aerosols in the atmosphere that are capable of attracting water at relative humidities below 90% and forming extremely small droplets... we observe these droplets as haze.
water having a temperature below the melting point of ice yet still existing in a liquid form (when saturation occurs between 0 degrees C and -4 degrees C the surplus water vapor condenses to form supercooled water)
(rare in the atmosphere) just as the formation of liquid droplets require condensation nuclei, the formation of ice chrystals at temperatures near 0 degrees C require ice nuclei
measures humidity (simple and most widely used), consists of a pair of thermometers.
wet bulb/dry bulb thermometers
mounted to a pivoting device, are circulated through the air, measures humidity.
wet bulb depression
the difference between wet bulb and dry bulb temperatures depending on the moisture content of the air.
use fans to circulate air around the psychometer (as opposed to being circulated)
human hair, expands and contracts on response to relative humidity.
continuous measure of humidity
heat index (apparent temperature)
expresses the effect of high humidity and high temperatures
(one of 2 air temperature changes) a process in which energy is added to or removed from a system [as opposed adiabatic process]
(one of 2 air temperature changes) a process in which temperature changes but no heat is added or removed from a substance [as opposed to diabatic process]
second law of thermodynamics
dictates that energy moves from regions of higher to lower temperatures.
dry adiabatic lapse rate (DALR)
the rate at which a rising parcel of unsaturated air cools
lifting condensation level (LCL)
the altitude at which condensation or deposition occurs when a parcel of air rises high enough to be cooled, lowering its temperature to the dew or frost point.
saturated adiabatic lapse rate (SALR)
the rate at which saturated air cools (saturated air cools at a slower rate than unsaturated air)
environmental lapse rate (ELR)
the vertical change in temperature through still air
liquid condensation on a surface
ice chrystals on a surface (much like dew, only at temperatures below 0 degrees C)
dew forms at slightly above 0 degrees C, the lower temperatures come in a freeze that dew. (different from frost)
radiation fogs (ground fogs)
occur when nighttime loss of longwave radiation causes colling to the dew point.
form when warm, moist air travels horizontally over a cooler surface ("advection" refers to horizontal)
(caused by adiabatic cooling) air flows along a gently soping surface, expands and cools as it moves upwards.