Geo題(why is weather so important to us?)

Weather is a term that encompasses phenomena in the atmosphere of a planet. The term is normally taken to mean the activity of these phenomena over short periods of time, usually no more than a few days. Average atmospheric conditions over significantly longer periods are known as climate. Usage of the two terms often overlaps and the physical concepts underlying them are closely related.

Basic mechanism

Cumulus clouds over AlbertaWhen used without qualification, "weather" is understood to be the weather of Earth. At large scales, weather results from temperature differences around the globe, which arise mainly because areas closer to the tropics receive more energy per unit area from the Sun than regions nearer to the Earth's poles. On local scales, temperature differences can occur because different surfaces (such as oceans, forests, or ice sheets) have major differing physical characteristics such as reflectivity (albedo), roughness, or moisture content.

Surface temperature differences in turn cause pressure differences. A hot surface heats the air above it and the air expands, lowering the air pressure. The result is a horizontal pressure gradient which accelerates the air from high to low pressure, creating wind. The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena. A large scale example of this process can be seen in the Hadley cell and other forms of atmospheric circulation. A smaller scale example would be coastal breezes.

Because the Earth's axis is tilted (not perpendicular to its orbital plane), sunlight is incident at different angles at different times of the year. In June the Northern Hemisphere is tilted towards the sun, so at any given Northern Hemisphere latitude sunlight falls more directly on that spot than in December (see Effect of sun angle on climate). This effect causes seasons. Over very long periods of time, ranging from thousands to hundreds of thousands of years, changes in Earth's orbital parameters will affect the amount of solar energy received by the Earth and influence long-term climate (see Milankovitch cycles).

Terrestrial weather

Fair weather Cumulus cloudsOn Earth, regularly occurring weather phenomena include such things as wind, cloud, rain, snow, fog and dust storms. Less common events include natural disasters such as tornadoes, hurricanes and ice storms. Almost all familiar weather phenomena occur in the troposphere (the lower part of the atmosphere). Weather does occur in the stratosphere and does affect weather lower down in the troposphere, but the exact mechanisms are poorly understood [1].

The Earth's atmosphere is a chaotic system, so small changes to one part can have large effects elsewhere. This makes it very difficult to accurately predict weather changes more than a few days in advance, though weather forecasters are continually working to extend this limit through the scientific study of weather, Meteorology.

Chaos theory says that the slightest variation in the motion of the air will grow with time. This idea is sometimes called the butterfly effect, from the idea that the motions caused by the flapping wings of a butterfly eventually could produce marked changes in the state of the atmosphere. Because of this sensitivity to small changes it will never be possible to forecast perfectly, although there still is potential for vast improvement.

Weather so important to us because if the weather is very bad,we can not live in the world.