The weather is a set of all the phenomena occurring in a given atmosphere at a given time.[1] Weather phenomena lie in the hydrosphere and troposphere.[2][3] Weather refers to current activity, as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of time.[4] When used without qualification, "weather" is understood to be the weather of Earth.-- Weather Services-- Weather Plus-- NOAA
-- Maps And Geography-- MapBlast-- Google Maps-- Yahoo Maps
Weather occurs due to density (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. 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 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 104 °F) annually. Over thousands to hundreds of thousands of years, changes in Earth's orbit affect the amount and distribution of solar energy received by the Earth and influence long-term climate.
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, 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.
Part of the Nature series on
Weather
Seasons
Temperate
Spring · Summer
Autumn · Winter
Tropical
Dry season
Wet season
Storms
Thunderstorm · Tornado
Tropical cyclone (Hurricane)
Extratropical cyclone
Winter storm · Blizzard
Ice storm
Precipitation
Fog · Drizzle · Rain
Freezing rain · Ice pellets
Hail · Snow · Graupel
Topics
Meteorology
Weather forecasting
Climate · Air pollution
Cause
Stratocumulus perlucidus cloudsOn Earth, common weather phenomena include 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).[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 density (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 you lie, 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 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).[9] 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).[10]
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 Earth's 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] Chaos theory says that the slightest variation in the motion of the ground can 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 make perfect forecasts, although there still is much potential for improvement.
The sun and oceans can also affect the weather of land. If the sun heats up ocean waters for a period of time, water can evaporate. Once evaporated into the air, the moisture can spread throughout nearby land, thus making it cooler.
Shaping the planet Earth
Main article: Weathering
Weather is one of the fundamental processes that shape the Earth. The process of weathering breaks down rocks and soils into smaller fragments and then into their constituent substances.[18]
These are then free to take part in chemical reactions that can affect the surface further (such as acid rain) or are reformed into other rocks and soils. In this way, weather plays a major role in erosion of the surface.[19]
Effect on humans
New Orleans, Louisiana, after being struck by Hurricane Katrina. Katrina was a Category 3 hurricane when it struck although it had been a category 5 hurricane in the Gulf of Mexico.Weather has played a large and sometimes direct part in human history. Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and the formation of land bridges during glacial 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 of Kublai Khan by the Kamikaze winds in 1281.[20] French claims to Florida came to an end in 1565 when a hurricane destroyed the French fleet, allowing Spain to conquer Fort Caroline.[21] More recently, Hurricane Katrina redistributed over one million people from the central Gulf coast elsewhere across the United States, becoming the largest diaspora in the history of the United States.[22]
Though weather affects people in drastic ways, it can also affect the human race in simpler ways. The human body is negatively affected by extremes in temperature, humidity, and wind.[23]
Mood is also affected by the weather.[24]
Forecasting
Main article: Weather forecasting
Forecast of surface pressures five days into the future for the north Pacific, North America, and north Atlantic ocean.Weather forecasting is the application of science and technology to predict the state of the atmosphere 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.[25][26] Weather forecasts are made by collecting quantitative data about the current state of the atmosphere and using scientific understanding of atmospheric processes to project how the atmosphere will evolve.[27]
Once an all human endeavor based mainly upon changes in barometric pressure, current weather conditions, and sky condition,[28][29] forecast models are now used to determine future conditions. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases. The chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as the difference in current time and the time
for which the forecast is being made (the range of the forecast) increases. The use of ensembles and model consensus helps to narrow the error and pick the most likely outcome.[30][31][32]
There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property.[33] Forecasts based on temperature and precipitation are important to agriculture,[34][35][36][37] and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days.[38][39][40] On an everyday basis, people use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and
the wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.
Modification
The wish to control the weather is evident throughout human history: from ancient rituals intended to bring rain for crops to the U.S. Military Operation Popeye, an attempt to disrupt supply lines by lengthening the North Vietnamese monsoon. The most successful attempts at influencing weather involve cloud seeding; they include the fog- and low stratus dispersion techniques employed by major airports, techniques used to increase winter precipitation over mountains, and techniques to suppress hail.[41] A recent example of weather control was China's preparation
for the 2008 Summer Olympic Games. China shot 1,104 rain dispersal rockets from 21 sites in the city of Beijing in an effort to keep rain away from the opening ceremony of the games on Aug 8, 2008. Guo Hu, head of the Beijing Municipal Meteorological Bureau (BMB), confirmed the success of the operation with 100 millimeters falling in Baoding City of Hebei Province, to the southwest and Beijing's Fangshan District recording a rainfall of 25 millimeters. [42]
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:[41]
Acid rain, caused by industrial emission of sulfur dioxide and nitrogen oxides into the atmosphere, adversely effects freshwater lakes, vegetation, and structures.
Anthropogenic pollutants reduce air quality and visibility.
Climate change caused by human activities that emit greenhouse gases into the air is expected to affect the frequency of extreme weather events such as drought, extreme temperatures, flooding, high winds, and severe storms.[43]
The effects of inadvertent weather modification may pose serious threats to many aspects of civilization, including ecosystems, natural resources, food and fiber production, economic development, and human health.[44].
Extremes on Earth
Main articles: Extremes on Earth and List of weather records
Early morning sunshine over Bratislava, Slovakia.
The same area, just three hours later, after heavy snowfall.On Earth, temperatures usually range ±40 °C (±72 °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 (−129 °F), at Vostok Station, Antarctica on 21 July 1983. The hottest air temperature ever recorded was 57.7 °C (135.9 °F) at Al 'Aziziyah, Libya, on 13 September 1922.[45] The highest recorded average annual temperature was 34.4 °C (93.9 °F) at Dallol, Ethiopia.[46] The
coldest recorded average annual temperature was −55.1 °C (−67 °F) at Vostok Station, Antarctica.[47] The coldest average annual temperature in a permanently inhabited location is at Eureka, Nunavut, in Canada, where the annual average temperature is −19.7 °C (−3 °F).[48]
Extraterrestrial within the Solar System
Jupiter's Great Red SpotStudying how the weather works on other planets has been seen as helpful in understanding how it works on Earth.[49] Weather on other planets follows many of the same physical principles as weather on Earth, but occurs on different scales and in atmospheres having different chemical composition. The Cassini–Huygens mission to Titan discovered clouds formed from methane or ethane which deposit rain composed of liquid methane and other organic compounds.[50] Earth's atmosphere includes six latitudinal circulation zones, three in each
hemisphere.[51] In contrast, Jupiter's banded appearance shows many such zones,[52] Titan has a single jet stream near the 50th parallel north latitude,[53] and Venus has a single jet near the equator.[54]
One of the most famous landmarks in the Solar System, Jupiter's Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years.[55] On other gas giants, the lack of a surface allows the wind to reach enormous speeds: gusts of up to 600 metres per second (about 2,100 kilometres per hour (1,300 mph)) have been measured on the planet Neptune.[56] This has created a puzzle for planetary scientists. The weather is ultimately created by solar energy and the amount of energy received by Neptune is only about 1/900th of that received by Earth, yet the
intensity of weather phenomena on Neptune is far greater than on Earth.[57] The strongest planetary winds discovered so far are on the extrasolar planet HD 189733 b, which is thought to have easterly winds moving at more than 9,600 kilometres per hour (6,000 mph).[58]
Space weather
Aurora BorealisMain article: Space weather
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. Inconsistencies in this wind and larger events on the surface of the star, such as coronal mass ejections, form a system that has features analogous to conventional weather systems (such as pressure and wind) and is generally known as space weather. Coronal mass ejections have been tracked as far out in the solar system as Saturn.[59] The activity of this system can affect planetary atmospheres and occasionally surfaces. The interaction of the solar wind with the terrestrial atmosphere can produce spectacular aurorae,[60] and can play havoc with electrically sensitive systems such as electricity grids and radio signals Source: Wikipedia
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes.
Many maps are static two-dimensional, geometrically accurate representations of three-dimensional space, while others are dynamic or interactive, even three-dimensional. Although most commonly used to depict geography, maps may represent any space, real or imagined, without regard to context or scale; e.g. Brain mapping, DNA mapping, and extraterrestrial mapping.
Geographic maps
A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit.Cartography, or map-making is the study and, often, practice, of crafting representations of the Earth upon a flat surface (see History of cartography), and one who makes maps is called a cartographer.
Road maps are perhaps the most widely used maps today, and form a subset of navigational maps, which also include aeronautical and nautical charts, railroad network maps, and hiking and bicycling maps. In terms of quantity, the largest number of drawn map sheets is probably made up by local surveys, carried out by municipalities, utilities, tax assessors, emergency services providers, and other local agencies. Many national surveying projects have been carried out by the military, such as the British Ordnance Survey (now a civilian government agency
internationally renowned for its comprehensively detailed work).
A map can also be any document giving information as to where or what something is.
Orientation of maps
The Hereford Mappa Mundi, about 1300, Hereford Cathedral, England. A classic "T-O" map with Jerusalem at centre, east toward the top, Europe the bottom left and Africa on the right.The term orientation refers to the relationship between directions on a map and compass directions. The word orient is derived from oriens, meaning east. In the Middle Ages many maps, including the T and O maps, were drawn with east at the top. Today the most common, but far from universal, cartographic convention is that North is at the top of a map. Examples of maps not oriented to north are:
Reversed maps, also known as Upside-Down maps or South-Up maps, which generally show Australia and New Zealand at the top of the map instead of the bottom.
Polar maps of the Arctic or Antarctic regions are conventionally centred on the pole, in which case the direction north would be towards or away from the centre of the map, respectively.
Buckminster Fuller's Dymaxion maps are based on a projection of the Earth's sphere onto an icosahedron. The resulting triangular pieces may be arranged in any order or orientation.
Maps from non-Western traditions are oriented a variety of ways. Old maps of Edo show the Japanese imperial palace as the "top", but also at the centre, of the map. Labels on the map are oriented in such a way that you cannot read them properly unless you put the imperial palace above your head.[]
Medieval European T and O maps such as the Hereford Mappa Mundi were centred on Jerusalem with east at the top. Indeed, prior to the reintroduction of Ptolemy's Geography to Europe around 1400, there was no single convention in the West. Portolan charts, for example, are oriented to the shores they describe.
Route and channel maps have traditionally been oriented to the road or waterway they describe.
Many maps used in the Society for Creative Anachronism show the west at the top, in honour of the Society starting in California.[]
Scale and accuracy
Many but not all maps are drawn to a scale, expressed as a ratio such as 1:10,000, meaning that 1 of any unit of measurement on the map corresponds to 10,000 of that same unit in reality. This allows the reader to estimate the sizes of, and distances between, depicted objects. A larger scale (i.e. the second number of the ratio is smaller) shows more detail and supports more accurate estimates, thus requiring a larger map to show the same area. Highly detailed maps covering areas ranging upward in size from small cities or counties to entire countries or continents are now
often published as books, or computer software (with numerous tools to aid the user, including user-adjustable scale and customized search engines), for convenient handling. Printed versions may include a comprehensive index, tables of distances between cities, and possibly even a cross reference of important destinations.
Computer software based maps provide numerous tools to aid the user, including user-adjustable scale (a.k.a "zoom") and customized search engines to locate street addresses.
Historically, large maps were presented (but not necessarily published, due to prohibitive labor costs) as scrolls, a famous example of which is the recently rediscovered hand-made copy of the Tabula Peutingeriana[1].
For modern examples, published maps designed for the hiker (e.g. USGS Topographic maps, a.k.a. "Topos") are often scaled at the ratio of approximately 1:25,000[citation needed], while maps designed for the motorist to display major highways might be scaled at 1:250,000 or 1:1,000,000[citation needed]. In any case, a properly made map will either state its scale, or declare that it is not scaled and can not be reliably used to deduce distances.
Cartogram: The EU distorted to show population distributions.Maps which use some quality other than physical area to determine relative size are called cartograms.
A famous (non-cartogram) example of a map without scale is the London Underground map, which best fulfills its purpose by being less physically accurate and more visually communicative to the hurried glance of the commuter. This is not a cartogram (since there is no consistent measure of distance) but a topological map that also depicts approximate bearings. The simple maps shown on some directional road signs are further examples of this kind.
In fact, most commercial navigational maps, such as road maps and town plans, sacrifice an amount of accuracy in scale to deliver a greater visual usefulness to its user, for example by exaggerating the width of roads. With the end-user similarly in mind, cartographers will censor the content of the space depicted by a map in order to provide a useful tool for that user. For example, a road map may or may not show railroads, smaller waterways or other prominent non-road objects, and if it does, it may show them less clearly (e.g. dashed or dotted lines/outlines of
various colors) than highways. Known as decluttering, the practice makes the subject matter the user is interested in easier to read, usually without sacrificing measurement accuracy. Software-based maps often allow the user to toggle decluttering between ON, OFF and AUTO as needed. In AUTO the degree of decluttering is adjusted as the user changes the scale being displayed.
Topographic maps, show elevation above (or depression below) sea level as contour lines, a specific type of Isoline. Isolines on any map or chart indicate the constant labeled value, such as elevation, temperature, or rainfall, for that particular line. Depending on the type of a map, alternative representations of elevation (or depression) exist as well.
World maps and projections
Main article: World map
Map of large underwater features. (1995, NOAA)Maps of the world or large areas are often either 'political' or 'physical'. The most important purpose of the political map is to show territorial borders; the purpose of the physical is to show features of geography such as mountains, soil type or land use. Geological maps show not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures.
Maps that depict the surface of the Earth also use a projection, a way of translating the three-dimensional real surface of the geoid to a two-dimensional picture. Perhaps the best-known world-map projection is the Mercator Projection, originally designed as a form dtof nautical chart.
Airplane pilots use aeronautical charts based on a Lambert conformal conic projection, in which a cone is laid over the section of the earth to be mapped. The cone intersects the sphere (the earth) at one or two parallels which are chosen as standard lines. This allows the pilots to plot a great-circle route approximation on a flat, two-dimensional chart.
Azimuthal or Gnomonic map projections are often used in planning air routes due to their ability to represent great circles as straight lines. Reginald Buckminster Fuller patented one such Gnomonic projection in 1946 as the Dymaxion Map.
Richard Edes Harrison produced a striking series of maps during and after World War II for Fortune magazine. These used "bird's eye" projections to emphasize globally strategic "fronts" in the air age, pointing out proximities and barriers not apparent on a conventional rectangular projection of the world.
Electronic maps
A USGS digital raster graphic.From the last quarter of the 20th century, the indispensable tool of the cartographer has been the computer. Much of cartography, especially at the data-gathering survey level, has been subsumed by Geographic Information Systems (GIS). The functionality of maps has been greatly advanced by technology simplifying the superimposition of spatially located variables onto existing geographical maps. Having local information such as rainfall level, distribution of wildlife, or demographic data integrated within the map allows more efficient analysis and better decision making. In the pre-electronic age such superimposition of data led Dr. John Snow to discover the cause of cholera. Today, it is used by agencies as diverse as wildlife conservationists and militaries around the world.
Even when GIS is not involved, most cartographers now use a variety of computer graphics programs to generate new maps.
Interactive, computerised maps are commercially available, allowing users to zoom in or zoom out (respectively meaning to increase or decrease the scale), sometimes by replacing one map with another of different scale, centred where possible on the same point. In-car satellite navigation systems are computerised maps with route-planning and advice facilities which monitor the user's position with the help of satellites. From the computer scientist's point of view, zooming in entails one or a combination of:
replacing the map by a more detailed one
enlarging the same map without enlarging the pixels, hence showing more detail by removing less information compared to the less detailed version
enlarging the same map with the pixels enlarged (replaced by rectangles of pixels); no additional detail is shown, but, depending on the quality of one's vision, possibly more detail can be seen;
if a computer display does not show adjacent pixels really separate, but overlapping instead (this does not apply for an LCD, but may apply for a cathode ray tube), then replacing a pixel by a rectangle of pixels does show more detail. A variation of this method is interpolation.
For example:
Typically (2) applies to a Portable Document Format (PDF) file or other format based on vector graphics. The increase in detail is, of course, limited to the information contained in the file:
enlargement of a curve may eventually result in a series of standard geometric figures such as straight lines, arcs of circles or splines.
(2) may apply to text and (3) to the outline of a map feature such as a forest or building.
(1) may apply to the text (displaying labels for more features), while (2) applies to the rest of the image. Text is not necessarily enlarged when zooming in. Similarly, a road represented by a double line may or may not become wider when one zooms in.
The map may also have layers which are partly raster graphics and partly vector graphics. For a single raster graphics image (2) applies until the pixels in the image file correspond to the pixels of the display, thereafter (3) applies.
See also Webpage (Graphics), PDF (Layers), Mapquest, Google Maps, Google Earth or Yahoo! Maps.
Labeling
To communicate spatial information effectively, features such as rivers, lakes, and cities need to be labeled. Over centuries cartographers have developed the art of placing names on even the densest of maps. Text placement or name placement can get mathematically very complex as the number of labels and map density increases. Therefore, text placement is time-consuming and labor-intensive, so cartographers and GIS users have developed automatic label placement to ease this process.[2][3]
Footnotes
^ BBC NEWS | Europe | Ancient Roman road map unveiled
^ Imhof, E., “Die Anordnung der Namen in der Karte,” Annuaire International de Cartographie II, Orell-Füssli Verlag, Zürich, 93-129, 1962.
^ Freeman, H.,, Map data processing and the annotation problem, Proc. 3rd Scandinavian Conf. on Image Analysis, Chartwell-Bratt Ltd. Copenhagen,