Evaporation: change from liquid to gaseous state
Transpiration: evaporation which occurs through plants (important in vegetated areas; ususally combined with evaporation to make evapotranspiration)
Sublimation: change from solid to gaseous state
Condensation: change from gaseous to liquid state
Solidification: change from liquid to solid state
Latent heat of Fusion (solid-liquid) = 79.7 calories/g
Latent heat of Vaporization (liquid-gas) = 540 calories/g
This is reason why sweating will help cool body, as water on skin surface will absorb 540 cal/g of water evaporated
Conversely, when water vapor condenses, 540 calories is released; and when water freezes, 79.7 calories is released per gram of water
This released energy is what creates winds, storms, lighting, etc.
Saturation concentration of water vapor in air varies with air temperature, so that cold air can hold much less water vapor than warm air
Creating saturation can occur in a number of ways:
First, by increasing the amount of water vapor in the air. However, this requires movements of air masses, and will take hours to days to happen.
Second, by keeping water vapor levels constant, but changing the temperature. Warm air which is not saturated will become so if the temperature falls. This happens when air rises.
The three major ways in which this can occur are:
(1) convection (fair weather summer clouds)
(2) frontal boundaries (cold front, warm front)
(3) orographic lifting (air moving up a mountain slope)
This last method is responsible for the formation of rain shadows in mountainous regions. When moist air is pushed up a mountain by prevailing winds, the air cools, relative humidity reaches 100%, and clouds form. These clouds create rain, which takes water out of the atmosphere. As air decends the downwind side of the mountain, the temperature of this water-depleted increases. Relative humidity falls to much less than saturation, clouds disappear, and rain fall decreases. At the latitude of the US and Europe, prevailing winds are from teh west. Thus, rainshadows are more pronounced on the eastern sides of mountains. However, at more southerly latitudes (Mexico, for instance), prevailing winds are from the east, creating rain shadows on the western side of mountains.
V. Groundwater resources. When rainfall exceeds evapotranspiration, some of the excess water is drawn by gravity into the ground. Approximately 95% of the liquid water on land occurs as groundwater.
Zone of aeration = region in soil horizon in which air is found in spaces between particles
Zone of saturation = region in soil horizon in which all of spaces between particles are filled with water
Water table = the line which separates the zones of aeration and saturation
Aquifer = layer of sediment or rock that is permiable and transmits water
An artesian well is formed when an aquifer is sandwiched between inpermiable layers, allowing pressure to develop on water in an aquifer
Points of discharge occur when groundwater or aquifers intersect the ground surface
Rates of groundwater flow are quite low (50 feet per year). As such, it is possible to remove groundwater more rapidly than it can be replaced. This can cause nearby shallow wells or springs to run dry.
Created 2 September 2011, Last Update 02 September 2011
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