Water Cycle
The water cycle, also known as the hydrologic cycle or the H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth.
The water cycle involves the exchange of energy, which leads to temperature changes. For instance, when water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment. These heat exchanges influence climate
The sun, which drives the water cycle, heats water in oceans and seas. Water evaporates as water vapour into the air. Ice, rain and snow can sublimate directly into water vapour. Evapotranspiration is water transpired from plants and evaporated from the soil. Water vapour molecule H2O, has less density compared to the major components of the atmosphere, nitrogen and oxygen, N2 and O2.
Due to the significant difference in molecular mass, water vapour in gas form gain height in open air as a result of buoyancy. However, as altitude increases, air pressure decrease and temperature drops
The lowered temperature causes water vapour to condense into a tiny liquid water droplet which is heavier than the air, such that it falls unless supported by an updraft. A huge concentration of these droplets over a large space up in the atmosphere become visible as cloud. Fog is formed if the water vapour condense near ground level, as a result of moist air and cool air collision or an abrupt reduction in air pressure.
Some precipitation falls as snow or hail, sleet, and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Most water falls back into the oceans or onto land as rain, where the water flows over the ground as surface runoff.
keywords:
Evaporation: The process by which water is changed from liquid to a gas or vapor
Sublimation: The changing of snow or ice to water vapor without melting
Evapotranspiration: The process by which water vapor is discharged to the atmosphere as a result of evaporation from the soil and transpiration by plants.
Condensation: The process by which water is changed from vapor to liquid
Precipitation: The discharge of water, in liquid or solid state, out of the atmosphere, generally upon a land or water surface
So. how we can relate water cycle with cloud seeding? How it works?
Cloud seeding
Cloud seeding, a form of weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the micro physical processes within the cloud. The most common chemicals used for cloud seeding include silver iodide, potassium iodide and dry ice (solid carbon dioxide). Liquid propane, which expands into a gas, has also been used. This can produce ice crystals at higher temperatures than silver iodide. After promising research, the use of hygroscopic materials, such as table salt, is becoming more popular. Introduction of a substance such as silver iodide, which has a crystalline structure similar to that of ice, will induce freezing nucleation. In mid-latitude clouds, the usual seeding strategy has been based on the fact that the equilibrium vapor pressure is lower over ice than over water. The formation of ice particles in super cooled clouds allows those particles to grow at the expense of liquid droplets. If sufficient growth takes place, the particles become heavy enough to fall as precipitation from clouds that otherwise would produce no precipitation. |
Haze
How we can relate cloud seeding and haze? Is it good? Is it bad? In my opinion, cloud seeding is good for it stimulates the formation of rains. Plus, it will casts out the haze temporarily. But the problem is when the rain stop, the haze come again and again and again and at this stage where the haze is very worse, I suggest that the haze will be worsen by cloud seeding. This is due to the substances we used in cloud seeding such as silver iodide which then take up water and undergo condensation to form droplets of water referred as rain. At the same time they produce acidic particles such as nitrogen oxide, sulphur dioxide and carbon dioxide which referred as haze. This also causes acid rain which give rises to many problems on earth such as skin disease, cancer, high acidity of soil and so on.
Group discussion in the class :)