• Precipitation
  • All liquid or solid phase aqueous particles that originate in the atmosphere and fall to the earth's surface.
  • Snow/Ice
Abstract from DBPedia
    In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzling, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor (reaching 100% relative humidity), so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation but colloids, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers. Moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is typically active when freezing rain occurs. A stationary front is often present near the area of freezing rain and serves as the focus for forcing and rising air. Provided there is necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely nimbostratus and cumulonimbus if significant precipitation is involved. Eventually, the cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow is possible within a cyclone's comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation occurs within the tropics and is caused by convection. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah regions. Precipitation is a major component of the water cycle, and is responsible for depositing fresh water on the planet. Approximately 505,000 cubic kilometres (121,000 cu mi) of water falls as precipitation each year: 398,000 cubic kilometres (95,000 cu mi) over oceans and 107,000 cubic kilometres (26,000 cu mi) over land. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres (39 in), but over land it is only 715 millimetres (28.1 in). Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Global warming is already causing changes to weather, increasing precipitation in some geographies, and reducing it in others, resulting in additional extreme weather. Precipitation may occur on other celestial bodies. Saturn's largest satellite, Titan, hosts methane precipitation as a slow-falling drizzle, which has been observed as Rain puddles at its equator and polar regions.

    降水(こうすい)とは、水蒸気が凝結して大気中において形成される液体または固体の水が、重力により落下する現象を指す気象学用語。降水現象ともいう。気象現象の1つであり、大気水象(hydrometeor)に分類される。地球上の水循環サイクルの1部分であり、大気から陸上や海洋への水の移動を担う。個々には、雨、雪、霙(みぞれ)、霰(あられ)、雹(ひょう)などが含まれる。霧、靄(もや)はそれらを構成する水滴が小さく浮遊しており、また霜は大気中の水蒸気が物体表面に直接昇華して起こるため、それぞれ降水には含まれない。 地上における(厳密には海上も含める)降水の量は降水量で表される。また、降水現象が一定時間に起こる確率を予報する手法を降水確率予報といい、日本では一定時限(ある時間帯内)に積算1mm以上の降水がある確率を降水確率という。 降水の観測方法はいくつかある。定量的な観測では雨量計を用いる。アメダスに採用されている転倒ます型雨量計は内蔵ヒーターが雪などを溶かして観測できる仕組みとなっている。雨が降っているがどうか(降り出し・降り止み)の観測には目視のほか、計器ではを用いる。降水の形態、特に雪・霙・霰・雹などを観測・区別する方法は目視が中心である。広い範囲の降水を面的に観測する方法として気象レーダーがあり、降水の分布や強度を観測でき、連続観測により降水の移動や変化を観測・推測できる。


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