Weather

Thunderstorm near Garajau, Madeira

Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy.[1] Most weather phenomena occur in the lowest level of the atmosphere, the troposphere,[2][3] just below the stratosphere. Weather refers to day-to-day temperature and precipitation activity, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time.[4] When used without qualification, "weather" is generally understood to mean the weather of Earth.

Weather is driven by air pressure, temperature and moisture differences between one place and another. These differences can occur due to the sun's angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley Cell, the Ferrel Cell, the Polar Cell, and the jet stream. Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by the Earth, thus influencing long-term climate and global climate change.

Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes, as most atmospheric heating is due to contact with the Earth's surface while radiative losses to space are mostly constant. 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 Earth's weather system is a chaotic system; as a result, 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 history, and there is evidence that human activities such as agriculture and industry have 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, Jupiter's 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 star's 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.

Causes

Cumulus mediocris cloud surrounded by stratocumulus

On Earth, the 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 the spread of the sunlight over a greater surface.[6] The strong temperature contrast between polar and tropical air gives rise to the large scale atmospheric circulation cells and 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.

2015 – Warmest Global Year on Record (since 1880) – Colors indicate temperature anomalies (NASA/NOAA; 20 January 2016).[9]

Because the Earth's 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).[10] This effect causes seasons. Over thousands to hundreds of thousands of years, changes in Earth's orbital parameters affect the amount and distribution of solar energy received by the Earth and influence long-term climate. (See Milankovitch cycles).[11]

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.[12] Higher altitudes are typically cooler than lower altitudes, which the result of higher surface temperature and radiational heating, which produces the adiabatic lapse rate.[13][14] In some situations, the temperature actually increases with height. This phenomenon is known as an inversion and can cause mountaintops to be warmer than the valleys below. Inversions can lead to the formation of fog and often act as a cap that suppresses thunderstorm development. 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 warms the air above it causing it to expand and lower the density and the resulting surface air pressure.[15] The resulting horizontal pressure gradient moves the air from higher to lower pressure regions, creating a wind, and the Earth's rotation then causes deflection of this air flow due to the Coriolis effect.[16] 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. As a result, small changes to one part of the system can accumulate and magnify to cause large effects on the system as a whole.[17] This atmospheric instability makes weather forecasting less predictable than tides or eclipses.[18] Although it is difficult to accurately predict weather more than a few days in advance, weather forecasters are continually working to extend this limit through meteorological research and refining current methodologies in weather prediction. However, 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.[19]

Other Languages
Alemannisch: Wetter
Ænglisc: Weder
العربية: طقس
aragonés: Orache
বাংলা: আবহাওয়া
Bân-lâm-gú: Thiⁿ-khì
башҡортса: Һауа торошо
беларуская: Надвор’е
беларуская (тарашкевіца)‎: Надвор’е
भोजपुरी: मौसम
Boarisch: Weda
bosanski: Vrijeme (klima)
Чӑвашла: Çанталăк
čeština: Počasí
Cymraeg: Tywydd
dansk: Vejr
Deutsch: Wetter
eesti: Ilm
Ελληνικά: Καιρός
Esperanto: Vetero
euskara: Eguraldi
فارسی: آب‌وهوا
føroyskt: Veður
Gàidhlig: Aimsir
ગુજરાતી: હવામાન
गोंयची कोंकणी / Gõychi Konknni: हवामान
한국어: 기상
հայերեն: Եղանակ
हिन्दी: मौसम
hrvatski: Vrijeme (klima)
Bahasa Indonesia: Cuaca
Iñupiak: Siḷa
íslenska: Veður
עברית: מזג אוויר
Basa Jawa: Cuaca
kalaallisut: Silasiorneq
ಕನ್ನಡ: ಹವಾಮಾನ
къарачай-малкъар: Кюнню халы
ქართული: ამინდი
kaszëbsczi: Wiodro
қазақша: Ауа райы
Kiswahili: Hali ya hewa
Кыргызча: Аба ырайы
Latina: Status caeli
latviešu: Laikapstākļi
Lëtzebuergesch: Wieder
lietuvių: Orai
Limburgs: Waer
magyar: Időjárás
मैथिली: मौसम
മലയാളം: കാലാവസ്ഥ
मराठी: हवामान
მარგალური: ტაროსი
Bahasa Melayu: Cuaca
монгол: Цаг агаар
नेपाली: मौसम
日本語: 気象
Nordfriisk: Weder
norsk nynorsk: Vêr
occitan: Temps (clima)
oʻzbekcha/ўзбекча: Ob-havo
ਪੰਜਾਬੀ: ਮੌਸਮ
پنجابی: موسم
Papiamentu: Wèr
Patois: Weda
polski: Pogoda
Qaraqalpaqsha: Hawa rayı
română: Vreme
русиньскый: Хвіля
русский: Погода
саха тыла: Күн-дьыл туруга
Scots: Wather
Seeltersk: Weeder
Sesotho sa Leboa: Boso
shqip: Moti
සිංහල: කාලගුණය
Simple English: Weather
سنڌي: موسم
slovenčina: Počasie
slovenščina: Vreme
کوردی: کەش
srpskohrvatski / српскохрватски: Vrijeme (klima)
suomi: Sää
svenska: Väder
தமிழ்: வானிலை
татарча/tatarça: Һава торышы
తెలుగు: పవనస్థితి
Türkçe: Hava durumu
українська: Погода
اردو: موسم
vepsän kel’:
Tiếng Việt: Thời tiết
Võro: Ilm
吴语: 天氣
Xitsonga: Maxelo
ייִדיש: וועטער
粵語: 天氣
žemaitėška: Uorā
中文: 天气
ГӀалгӀай: Хаоттам
Lingua Franca Nova: Clima