why is evaporation important to the water cycle

Cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the hydrologic cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle remains essentially constant, its distribution among the various processes is continually changing. Evaporation, one of the major processes in the cycle, is the transfer of water from the surface of the Earth to the atmosphere. By evaporation, water in the liquid state is transferred to the gaseous, or vapour, state. This transfer occurs when some molecules in a water mass have attained sufficient kinetic energy to eject themselves from the water surface. The main factors affecting evaporation are temperature, humidity, wind speed, and solar radiation. The direct measurement of evaporation, though desirable, is difficult and possible only at point locations. The principal source of water vapour is the oceans, but evaporation also occurs in soils, snow, and ice. Evaporation from snow and ice, the direct conversion from solid to vapour, is known as sublimation. Transpiration is the evaporation of water through minute pores, or stomata, in the leaves of plants. For practical purposes, transpiration and the evaporation from all water, soils, snow, ice, vegetation, and other surfaces are lumped together and called evapotranspiration, or total evaporation. Water vapour is the primary form of atmospheric moisture. Although its storage in the atmosphere is comparatively small, water vapour is extremely important in forming the moisture supply for dew, frost, fog, clouds, and precipitation. Practically all water vapour in the atmosphere is confined to the troposphere (the region below 6 to 8 miles [10 to 13 km] altitude).


The transition process from the vapour state to the liquid state is called condensation. Condensation may take place as soon as the air contains more water vapour than it can receive from a free water surface through evaporation at the prevailing temperature. This condition occurs as the consequence of either cooling or the mixing of air masses of different temperatures. By condensation, water vapour in the atmosphere is released to form precipitation. Precipitation that falls to the Earth is distributed in four main ways: some is returned to the atmosphere by evaporation, some may be intercepted by vegetation and then evaporated from the surface of leaves, some percolates into the soil by infiltration, and the remainder flows directly as surface runoff into the sea. Some of the infiltrated precipitation may later percolate into streams as groundwater runoff. Direct measurement of runoff is made by stream gauges and plotted against time on hydrographs. Most groundwater is derived from precipitation that has percolated through the soil. Groundwater flow rates, compared with those of surface water, are very slow and variable, ranging from a few millimetres to a few metres a day. Groundwater movement is studied by tracer techniques and remote sensing. Ice also plays a role in the hydrologic cycle. Ice and snow on the Earth s surface occur in various forms such as frost, sea ice, and glacier ice. When soil moisture freezes, ice also occurs beneath the Earth s surface, forming permafrost in tundra climates. About 18,000 years ago glaciers and ice caps covered approximately one-third of the Earth s land surface. Today, about 12 percent of the land surface remains covered by ice masses.


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Posted on April 17, 2012 in by Atmospheric icing occurs whenPwaterPdropletsPin thePatmospherePfreezePon objects they contact. This can be extremely dangerous toPaircraft, as the built-upPicePchanges thePaerodynamicsPof the flight surfaces, which can increase the risk of a subsequentPstallingPof thePairfoil. AnP avalanche Pis a sudden, rapid flow ofPsnowPdown a slope, occurring when either natural triggers, such as loading from new snow or rain, or artifical triggers, such as snowmobilers, explosives or backcountry skiers, overload the snowpack. A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth s atmosphere are studied in the cloud physics branch of meteorology. Two processes, possibly acting together, can lead to air s becoming saturated: cooling the air or adding water vapor to the air. In general, precipitation will fall to the surface; an exception is virga, which evaporates before reaching the surface. Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition. In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. A cyclone is a synonym for hurricane.


Most large-scale cyclonic circulations are centered on areas of low atmospheric pressure. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Dead water is the nautical term for a strange phenomenon which can occur when a layer of fresh or brackish water rests on top of denser salt water, without the two layers mixing. A ship powered by direct thrust under the waterline (such as a propeller), traveling in such conditions may be hard to maneuver or can even slow down almost to a standstill. Much of the energy from the ship s propeller only results in waves and turbulence between the two layers of water, leaving a ship capable of traveling at perhaps as little as 20% of its normal speed. P Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate, resulting in the formation of water droplets. When temperatures are low enough, dew takes the form of ice; this form is called frost (frost is, however, not frozen dew). Don Juan Pond is a shallow, flat-bottom, hyper-saline pond. It has greaterPsalinityPthan thePDead SeaPor evenPLake Assal. It has been claimed that the salinity in Don Juan Pond is over 18 times the ocean s salinity, compared to that of the Dead Sea at about 8 times that of the ocean. The fact that it is the only one of the Antarctic hypersaline lakes that almost never freezes is an indication of its top rank in salinity among the world s lakes. Previous Post

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