Weather refers to the state of the Earth'satmosphere at a specific place and time, typically described in terms of temperature, humidity,cloud cover, andstability.[1] OnEarth, most weather phenomena occur in the lowest layer of the planet'satmosphere, thetroposphere,[2][3] just below thestratosphere. Weather refers to day-to-day temperature,precipitation, and other atmospheric conditions, whereasclimate 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.
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 theatmosphere for a future time and a given location. Earth's weather system is achaotic 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 tocontrol the weather have occurred throughout history, and there is evidence thathuman 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 theSolar System, Jupiter'sGreat Red Spot, is ananticyclonic storm known to have existed for at least 300 years. However, the weather is not limited to planetary bodies. Astar'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 theSun is known as thesolar wind.
OnEarth, commonweather phenomena include wind,cloud, rain, snow,fog anddust storms. Some more common events includenatural disasters such astornadoes,hurricanes,typhoons andice 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 andmoisture differences from one place to another. These differences can occur due to thesun angle at any particular spot, which varies by latitude in 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 spread of thesunlight over a greater surface.[6] The strong temperature contrast betweenpolar and tropical air gives rise to the large scaleatmospheric circulation cells and thejet stream.[7] Weathersystems in the mid-latitudes, such asextratropical cyclones, are caused by instabilities of thejet stream flow (seebaroclinity).[8] Weather systems in the tropics, such asmonsoons or organizedthunderstorm systems, are caused by different processes.
2015 –5th Warmest Global Year on Record (since 1880) as of 2021 – Colors indicate temperature anomalies (NASA/NOAA; 20 January 2016).[9]
Because the Earth'saxis 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 theSun, so at any given Northern Hemisphere latitude sunlight falls more directly on that spot than in December (seeEffect 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 ofsolar energy received by theEarth and influence long-term climate. (SeeMilankovitch cycles).[11]
The uneven solar heating (the formation of zones of temperature and moisture gradients, orfrontogenesis) 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 is the result of higher surface temperature and radiational heating, which produces theadiabaticlapse rate.[13][14] In some situations, the temperature actually increases with height. This phenomenon is known as aninversion and can cause mountaintops to be warmer than the valleys below. Inversions can lead to the formation offog and often act as acap thatsuppresses thunderstorm development. On local scales, temperature differences can occur because different surfaces (such as oceans, forests,ice sheets, or human-made objects) have differing physical characteristics such asreflectivity, 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 surfaceair pressure.[15] The resulting horizontalpressure gradient moves the air from higher to lower pressure regions, creating a wind, and the Earth's rotation then causes deflection of this airflow due to theCoriolis effect.[16] The simple systems thus formed can then displayemergent behaviour to produce morecomplex systems and thus other weather phenomena. Large scale examples include theHadley cell while a smaller scale example would becoastal breezes.
Theatmosphere is achaotic 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 tidal waves 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 throughmeteorological research and refining current methodologies in weather prediction. However, it is theoretically impossible to make useful day-to-daypredictions more than about two weeks ahead, imposing an upper limit topotential for improved prediction skill.[19]
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.[20] 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 inchemical reactions that can affect the surface further (such asacid 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 inerosion of the surface.[21]
Weather, seen from an anthropological perspective, is something all humans in the world constantly experience through their senses, at least while being outside. There are socially and scientifically constructed understandings of what weather is, what makes it change, the effect the weather, and especiallyinclement weather, has on humans in different situations, etc.[22] Therefore, weather is something people often communicate about.
In the United States, theNational Weather Service has an annual report for fatalities, injury, and total damage costs which include crop and property. They gather this data via National Weather Service offices located throughout the 50 states in the United States as well as it's territories. As of 2019, tornadoes have had the greatest impact on humans with 42 fatalities while costing crop and property damage over 3 billion dollars.[23]
The weather has played a large and sometimes direct part inhuman history. Aside fromclimatic changes that have caused the gradual drift of populations (for example thedesertification of the Middle East, and the formation ofland bridges duringglacial periods),extreme weather events have caused smaller scale population movements and intruded directly in historical events. One such event is the saving of Japan from invasion by the Mongol fleet ofKublai Khan by theKamikaze winds in 1281.[24] French claims to Florida came to an end in 1565 when a hurricane destroyed the French fleet, allowing Spain to conquerFort Caroline.[25] More recently,Hurricane Katrina redistributed over one million people from the centralGulf coast elsewhere across the United States, becoming the largestdiaspora in the history of the United States.[26]
TheLittle Ice Age caused crop failures andfamines in Europe. During the period known as theGrindelwald Fluctuation (1560–1630), volcanic forcing events[27] seem to have led to more extreme weather events.[28] These included droughts, storms and unseasonal blizzards, as well as causing the SwissGrindelwald Glacier to expand. The 1690s saw the worst famine in France since the Middle Ages. Finland suffered a severe famine in 1696–1697, during which about one-third of the Finnish population died.[29]
Forecast of surface pressures five days into the future for the north Pacific, North America, and the north Atlantic Ocean as on 9 June 2008
Weather forecasting is the application of science and technology to predict the state of theatmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century.[30] Weather forecasts are made by collectingquantitative data about the current state of the atmosphere and usingscientific understanding of atmospheric processes to project how the atmosphere will evolve.[31]
Once an all-human endeavor based mainly upon changes inbarometric pressure, current weather conditions, and sky condition,[32][33]forecast models are now used to determine future conditions. On the other hand, human input is still required to pick the best possible forecast model to base the forecast upon, which involves many disciplines such as pattern recognition skills,teleconnections, knowledge of model performance, and knowledge of model biases.
Thechaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, the error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as of the difference in current time and the time for which the forecast is being made (therange of the forecast) increases. The use of ensembles and model consensus helps to narrow the error and pick the most likely outcome.[34][35][36]
There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property.[37][38] Forecasts based on temperature andprecipitation are important to agriculture,[39][40][41][42] and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days.[43][44][45]
In some areas, people use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavyrain,snow and thewind chill, forecasts can be used to plan activities around these events and to plan ahead to survive through them.
Tropical weather forecasting is different from that at higher latitudes. The sun shines more directly on the tropics than on higher latitudes (at least on average over a year), which makes the tropics warm (Stevens 2011). And, the vertical direction (up, as one stands on the Earth's surface) is perpendicular to the Earth's axis of rotation at the equator, while the axis of rotation and the vertical are the same at the pole; this causes the Earth's rotation to influence the atmospheric circulation more strongly at high latitudes than low latitudes. Because of these two factors, clouds and rainstorms in the tropics can occur more spontaneously compared to those at higher latitudes, where they are more tightly controlled by larger-scale forces in the atmosphere. Because of these differences, clouds and rain are more difficult to forecast in the tropics than at higher latitudes. On the other hand, the temperature is easily forecast in the tropics, because it does not change much.[46]
Modification
The aspiration tocontrol the weather is evident throughout human history: from ancient rituals intended to bring rain for crops to the U.S. MilitaryOperation Popeye, an attempt to disruptsupply lines by lengthening the North Vietnamesemonsoon. The most successful attempts at influencing weather involvecloud seeding; they include thefog- and lowstratus dispersion techniques employed by major airports, techniques used to increasewinter precipitation over mountains, and techniques to suppresshail.[47] A recent example of weather control was China's preparation for the2008 Summer Olympic Games. China shot 1,104 rain dispersal rockets from 21 sites in the city ofBeijing in an effort to keep rain away from the opening ceremony of the games on 8 August 2008. Guo Hu, head of the Beijing Municipal Meteorological Bureau (BMB), confirmed the success of the operation with 100 millimeters falling inBaoding City ofHebei Province, to the southwest and Beijing'sFangshan District recording a rainfall of 25 millimeters.[48]
Whereas there is inconclusive evidence for these techniques' efficacy, there is extensive evidence that human activity such as agriculture and industry results in inadvertent weather modification:[47]
Heat, generated by large metropolitan areas have been shown to minutely affect nearby weather, even at distances as far as 1,600 kilometres (990 mi).[50]
The effects of inadvertent weather modification may pose serious threats to many aspects of civilization, includingecosystems,natural resources, food and fiber production,economic development, and human health.[51]
Microscale meteorology
Microscale meteorology is the study of short-livedatmospheric phenomena smaller thanmesoscale, about 1 km or less. These two branches ofmeteorology are sometimes grouped together as "mesoscale and microscale meteorology" (MMM) and together study all phenomena smaller thansynoptic scale; that is they study features generally too small to be depicted on aweather map. These include small and generally fleeting cloud "puffs" and other small cloud features.[52]
Extremes on Earth
In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface[53]
On Earth, temperatures usually range ±40 °C (100 °F to −40 °F) annually. The range of climates and latitudes across the planet can offer extremes of temperature outside this range. The coldest air temperature ever recorded on Earth is −89.2 °C (−128.6 °F), atVostok Station, Antarctica on 21 July 1983. The hottest air temperature ever recorded was 57.7 °C (135.9 °F) atʽAziziya, Libya, on 13 September 1922,[54] but that reading wasdeemed illegitimate by theWorld Meteorological Organization. The highest recorded average annual temperature was 34.4 °C (93.9 °F) atDallol, Ethiopia.[55] The coldest recorded average annual temperature was −55.1 °C (−67.2 °F) atVostok Station, Antarctica.[56]
The coldest average annual temperature in a permanently inhabited location is atEureka, Nunavut, in Canada, where the annual average temperature is −19.7 °C (−3.5 °F).[57]
The windiest place ever recorded is in Antarctica,Commonwealth Bay (George V Coast). Here the gales reach 199 mph (320 km/h).[58] Furthermore, the greatestsnowfall in a period of twelvemonths occurred inMount Rainier, Washington, US. It was recorded as 31,102 mm (102.04 ft) of snow.[59]
Extraterrestrial weather
Jupiter's Great Red Spot in February 1979, photographed by the uncrewedVoyager 1 NASA space probe.
Studying how the weather works on other planets has been seen as helpful in understanding how it works on Earth.[60] Weather on other planets follows many of the same physical principles as weather onEarth, but occurs on different scales and in atmospheres having different chemical composition. TheCassini–Huygens mission toTitan discovered clouds formed from methane or ethane which deposit rain composed of liquidmethane and otherorganic compounds.[61] Earth's atmosphere includes six latitudinal circulation zones, three in each hemisphere.[62] In contrast,Jupiter's banded appearance shows many such zones,[63] Titan has a single jet stream near the 50th parallel north latitude,[64] andVenus has a single jet near the equator.[65]
One of the most famous landmarks in theSolar System, Jupiter'sGreat Red Spot, is ananticyclonic storm known to have existed for at least 300 years.[66] On othergiant planets, the lack of a surface allows the wind to reach enormous speeds: gusts of up to 600 metres per second (about 2,100 km/h or 1,300 mph) have been measured on the planetNeptune.[67] This has created a puzzle forplanetary scientists. The weather is ultimately created by solar energy and the amount of energy received by Neptune is only about1⁄900 of that received by Earth, yet the intensity of weather phenomena on Neptune is far greater than on Earth.[68] As of 2007[update], the strongest planetary winds discovered are on theextrasolar planetHD 189733 b, which is thought to have easterly winds moving at more than 9,600 kilometres per hour (6,000 mph).[69]
Weather is not limited to planetary bodies. Like all stars, theSun's corona is constantly being lost to space, creating what is essentially a very thinatmosphere throughout theSolar System. The movement of mass ejected from the Sun is known as thesolar wind. Inconsistencies in this wind and larger events on the surface of the star, such ascoronal mass ejections, form a system that has features analogous to conventional weather systems (such as pressure and wind) and is generally known asspace weather. Coronal mass ejections have been tracked as far out in theSolar System asSaturn.[70] The activity of this system can affect planetaryatmospheres and occasionally surfaces. The interaction of thesolar wind with the terrestrial atmosphere can produce spectacularaurorae,[71] and can play havoc with electrically sensitive systems such aselectricity grids and radio signals.[72]
^Crate, Susan A; Nuttall, Mark, eds. (2009).Anthropology and Climate Change: From Encounters to Actions(PDF). Walnut Creek, CA: Left Coast Press. pp. 70–86, i.e. the chapter 'Climate and weather discourse in anthropology: from determinism to uncertain futures' by Nicholas Peterson & Kenneth Broad.Archived(PDF) from the original on 27 February 2021. Retrieved21 May 2014.
^United States. National Weather Service. Office of Climate, Water, Weather Services, & National Climatic Data Center. (2000).Weather Related Fatality and Injury Statistics.
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