This article is about the atmospheric process. For the geological process, see Weathering and Erosion. For other uses see Weather (disambiguation), and Weather systems (disambiguation). Thunderstorm near Garajau, Madeira Part of the nature series Weather Calendar seasons Spring Summer Autumn Winter Tropical seasons Dry season Wet season Storms Thunderstorm (Thundersnow) Supercell Downburst Lightning Tornado Waterspout Tropical cyclone (Hurricane) Extratropical cyclone Winter storm Blizzard Ice storm Dust storm Firestorm Cloud Precipitation Drizzle (Freezing drizzle) Rain (Freezing rain) Snow Rain and snow mixed Snow grains Snow roller Graupel Ice pellets Hail Topics Meteorology Climate Cloud Weather forecasting Heat wave Air pollution Cold wave Portal icon Weather portal v t e Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy.[1] Most weather phenomena occur in the troposphere,[2][3] just below the stratosphere. Weather generally refers to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time.[4] When used without qualification, weather, is understood to mean the weather of Earth. Weather is driven by air pressure (temperature and moisture) differences between one place and another. These pressure and temperature differences can occur due to the sun angle at any particular spot, which varies by latitude from the tropics. The strong temperature contrast between polar and tropical air gives rise to the jet stream. Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earths axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On Earths surface, temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in Earths orbit affect the amount and distribution of solar energy received by the Earth and influence long-term climate and global climate change. Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes due to differences in compressional heating. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. The atmosphere is a chaotic system, so small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout human history, and there is evidence that human activity such as agriculture and industry has inadvertently modified weather patterns. Studying how the weather works on other planets has been helpful in understanding how weather works on Earth. A famous landmark in the Solar System, Jupiters Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years. However, weather is not limited to planetary bodies. A stars corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System. The movement of mass ejected from the Sun is known as the solar wind. Contents [hide] 1 Cause 2 Shaping the planet Earth 3 Major Wind and Pressure Systems and Related Weather 4 Effect on humans 4.1 Effects on populations 4.2 Effects on individuals 5 Forecasting 6 Modification 7 Microscale meteorology 8 Extremes on Earth 9 Extraterrestrial within the Solar System 10 Space weather 11 See also 12 References 13 External links Cause[edit] Stratocumulus perlucidus clouds On Earth, common weather phenomena include wind, cloud, rain, snow, fog and dust storms. Less common events include natural disasters such as tornadoes, hurricanes, typhoons and ice storms. Almost all familiar weather phenomena occur in the troposphere (the lower part of the atmosphere).[3] Weather does occur in the stratosphere and can affect weather lower down in the troposphere, but the exact mechanisms are poorly understood.[5] Weather occurs primarily due to air pressure (temperature and moisture) differences between one place to another. These differences can occur due to the sun angle at any particular spot, which varies by latitude from the tropics. In other words, the farther from the tropics one lies, the lower the sun angle is, which causes those locations to be cooler due to the indirect sunlight.[6] The strong temperature contrast between polar and tropical air gives rise to the jet stream.[7] Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow (see baroclinity).[8] Weather systems in the tropics, such as monsoons or organized thunderstorm systems, are caused by different processes. Because the Earths axis is tilted relative 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).[9] This effect causes seasons. Over thousands to hundreds of thousands of years, changes in Earths orbital parameters affect the amount and distribution of solar energy received by the Earth and influence long-term climate. (See Milankovitch cycles).[10] The uneven solar heating (the formation of zones of temperature and moisture gradients, or frontogenesis) can also be due to the weather itself in the form of cloudiness and precipitation.[11] Higher altitudes are cooler than lower altitudes, which is explained by the lapse rate.[12][13] On local scales, temperature differences can occur because different surfaces (such as oceans, forests, ice sheets, or man-made objects) have differing physical characteristics such as reflectivity, 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 and its density.[14] The resulting horizontal pressure gradient accelerates the air from high to low pressure, creating wind, and Earths rotation then causes curvature of the flow via the Coriolis effect.[15] The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena. Large scale examples include the Hadley cell while a smaller scale example would be coastal breezes. The atmosphere is a chaotic system, so small changes to one part of the system can grow to have large effects on the system as a whole.[16] This makes it difficult to accurately predict weather more than a few days in advance, though weather forecasters are continually working to extend this limit through the scientific study of weather, meteorology. It is theoretically impossible to make useful day-to-day predictions more than about two weeks ahead, imposing an upper limit to potential for improved prediction skill.[17] Shaping the planet Earth[edit] Main article: Weathering Weather is one of the fundamental processes that shape the Earth. The process of weathering breaks down the rocks and soils into smaller fragments and then into their constituent substances.[18] During rains precipitation, the water droplets absorb and dissolve carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic, which aids the erosive properties of water. The released sediment and chemicals are then free to take part in chemical reactions that can affect the surface further (such as acid rain), and sodium and chloride ions (salt) deposited in the seas/oceans. The sediment may reform in time and by geological forces into other rocks and soils. In this way, weather plays a major role in erosion of the surface.[19] Major Wind and Pressure Systems and Related Weather[edit] Region Name Pressure Surface Winds Weather Equator (0º) Doldrums (ITCZ) (equatorial low) Low Light, variable winds Cloudiness, abundant precipitation in all seasons; breeding ground for hurricanes. Relatively low sea-surface salinity because of high rainfall relative to evaporation 0º-30ºN and S Trade winds (easterlies) - Northeast in Northern Hemisphere; Southeast in Southern Hemisphere Summer wet, winter dry; pathway for tropical disturbances 30ºN and S Horse latitudes High Light, variable winds Little cloudiness; dry in all seasons. Relatively high sea-surface salinity because of high evaporation relative to precipitation 30º-60ºN and S Prevailing Westerlies - Southwest in Northern Hemisphere; Northwest in Southern Hemisphere Winter wet, summer dry; pathway for subtropical high and low pressure 60ºN and S Polar front Low Variable Stormy, cloudy weather zone; ample precipitation in all seasons 60º-90ºN and S Polar easterlies - Northeast in Northern Hemisphere; Southeast in Southern Hemisphere Cold polar air with very low temperatures 90ºN and S Poles High Southerly in Northern Hemisphere; Northerly in Southern Hemisphere Cold, dry air; sparse precipitation in all seasons
Posted on: Wed, 29 Jan 2014 10:52:02 +0000
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