weather, state of the atmosphere at a given time and place with regard to temperature, air pressure (see barometer barometer , instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long.
..... Click the link for more information. ), wind, humidity, cloudiness, and precipitation. The term weather is restricted to conditions over short periods of time; conditions over long periods, generally at least 30–50 years, are referred to as climate climate, average condition of the atmosphere near the earth's surface over a long period of time, taking into account temperature, precipitation (see rain), humidity, wind, barometric pressure, and other phenomena.
..... Click the link for more information. .

The earliest evidence of scientific activity in the field of meteorology meteorology, branch of science that deals with the atmosphere of a planet, particularly that of the earth, the most important application of which is the analysis and prediction of weather.
..... Click the link for more information. , the study of the earth's atmosphere, especially as it relates to weather forecasting, is from the 4th cent. B.C.; Aristotle wrote what is probably the first treatise on the subject. The first attempt to chart weather from reports over a considerable area was made (1820) in Europe by H. W. Brandes, but it was not until after the invention of the telegraph that the rapid collection of weather data from remote stations became possible.

In the United States, a government weather service was established (1870) under the army Signal Corps. In 1891 the weather service was transferred to the U.S. Weather Bureau under the Dept. of Agriculture, and it later came (1940) under the jurisdiction of the Dept. of Commerce. The U.S. Weather Bureau has since been renamed the U.S. National Weather Service and transferred to the National Oceanic and Atmospheric Administration. The central forecast office is the National Meteorological Center (NMC), in Suitland, Md.; first-order stations are located chiefly in the larger cities, and numerous substations for special purposes (e.g., observing river stages, measuring depth of snow, and maintaining records of climate) are distributed throughout the country.

Devices used for meteorological observations include rockets, weather satellites, radiosondes radiosonde , group of instruments for simultaneous measurement and radio transmission of meteorological data, including temperature, pressure, and humidity of the atmosphere.
..... Click the link for more information. , barometers, anemometers, weather vanes weather vane or wind vane, instrument used to indicate wind direction. It consists of an asymmetrically shaped object, e.g., an arrow or a rooster, mounted at its center of gravity so it can move freely about a vertical axis.
..... Click the link for more information. , psychrometers psychrometer , one of many instruments used for measuring the water vapor content or relative humidity of the atmosphere. It consists of two identical thermometers—the wet-bulb thermometer, so called because its bulb is covered with a jacket of tight-fitting
..... Click the link for more information. , thermometers thermometer, instrument for measuring temperature. Galileo and Sanctorius devised thermometers consisting essentially of a bulb with a tubular projection, the open end of which was immersed in a liquid.
..... Click the link for more information. , and radar radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency
..... Click the link for more information. . By means of high-speed telecommunications, information from all over the world is sent to the NMC, where the data is decoded and plotted. These data are used to create weather maps based on simultaneous weather observations at different atmospheric levels over any desired geographic region. On a typical map the various weather elements are shown by figures and symbols; isobars isobar or isobaric line , line drawn on a weather map through points of equal atmospheric pressure. Isobars are used to define cyclones (low-pressure regions) and anticyclones (high-pressure regions).
..... Click the link for more information. are drawn to show areas of low pressure (cyclones cyclone, atmospheric pressure distribution in which there is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the Coriolis effect, causes air to circulate about the core of lowest pressure in a
..... Click the link for more information. ) and high pressure (anticyclones); fronts front, in meteorology, zone of transition between adjacent air masses. If a cold air mass is advancing to replace a warmer one, their mutual boundary is termed a cold front; if the reverse, then the boundary is termed a warm front, whereas a stationary front
..... Click the link for more information. (boundaries between air masses air mass, large body of air within the earth's atmosphere in which temperature and humidity, although varying at different heights, remain similar throughout the body at any one height.
..... Click the link for more information. ) and areas of precipitation are indicated.

By using computer models based on mathematical formulations of the dynamics of the atmosphere, weather charts are also produced as prognostics of future weather patterns. The many simplifying assumptions required in these formulations, as well as the incompleteness of weather data, limit the accuracy of the computer predictions; though as advances in computer systems occur, these models are becoming more complete and, hence, more accurate. Meteorologists interpret and modify such prognostics according to their knowledge of the prognostics' reliability and their familiarity with local influences, such as topography and proximity to large bodies of water, in order to derive the best possible weather forecasts.

Forecasts are disseminated by television, radio, telephone, newspapers, and the Internet. Detailed forecasts can usually be made only for a short future period (generally 48 hr or less). Forecasts for up to five days can usually predict departures from normal temperature and precipitation fairly well; longer-range predictions are more general and less accurate, being based on the known normal weather of the area. Mathematical models, particularly those run on supercomputers, have helped to understand weather changes, including general global circulation patterns, and how perturbations in the atmosphere and oceans effect the weather.

Bibliography

See J. R. Eagleman, Weather Concepts and Terminology (1989); J. Farrand, Jr., Weather (1990); H. M. Conway and L. L. Liston, Weather Handbook (1990); R. C. McNeill, Understanding the Weather (1991).

weather

State of the atmosphere at a particular place during a short period of time. It involves day-to-day changes in such atmospheric phenomena as temperature, humidity, precipitation (type and amount), air pressure, wind, and cloud cover. Most weather occurs in the troposphere, but phenomena of the higher regions of the atmosphere, such as jet streams, and geographic features, most notably mountains and large bodies of water, also affect it. See also climate.

weather

a. the day-to-day meteorological conditions, esp temperature, cloudiness, and rainfall, affecting a specific place

b. relating to the forecasting of weather

2. make heavy weather (of a vessel) to roll and pitch in heavy seas

3. on or at the side or part towards the wind; windward
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weather [′weth·ər]

(meteorology)

The state of the atmosphere, mainly with respect to its effects upon life and human activities; as distinguished from climate, weather consists of the short-term (minutes to months) variations of the atmosphere.

As used in the making of surface weather observations, a category of individual and combined atmospheric phenomena which must be drawn upon to describe the local atmospheric activity at the time of observation.

weather

That portion of a wood shingle that is exposed to the elements.

Weather

the state of the atmosphere in a given place at a certain moment or during a limited period of time, such as a day, month, or year. The main trends in weather conditions over a long period of time are known as the climate. The meteorological elements that characterize weather include the pressure, temperature, and humidity of the air, the force and direction of the wind, the cloud cover, and the amount of sunshine. Atmospheric precipitation, visibility, and such phenomena as fog, snow storms, and thunderstorms also characterize weather. The understanding of weather has grown with the growth of economic activity. The development of aviation, for example, aided the understanding of weather in the free air and made such elements as visibility more important. Atmospheric precipitation, visibility, and such phenomena as fog, snowstorms, and thunderstorms also characterize weather. The understanding of weather has grown with the growth of economic activity. The development of aviation, for example, aided the understanding of weather in the free air and made such elements as visibility more important. Atmospheric turbulence, various electrical atmospheric phenomena, and the influx of solar radiation can be attributed to weather characteristics.

The weather undergoes continuous change on the earth’s surface. The change may be daily but can also be for a period of several days or even several minutes. Some changes are periodic and depend on the direct effect of solar radiation. Periodic changes are diurnal if they are affected by the earth’s rotation about its axis and annual if they are affected by the earth’s revolution around the sun. Diurnal variations in weather are especially pronounced close to the earth’s surface because changes in air temperature are dependent on the temperature of the earth’s surface. Humidity, cloudiness, precipitation, and wind are related, in turn, to air temperature. The amplitude of diurnal fluctuations in temperature, humidity, and wind velocity decreases rapidly with altitude. Annual variations in weather, manifested by the changing seasons, extend to high altitudes in both the troposphere and the stratosphere.

Nonperiodic changes in weather are especially significant in extratropical latitudes and are related to atmospheric circulation, that is, to the transfer of air masses to different regions of the earth (advection). In a given region, the transfer of air masses causes changes in the weather. The place of origin of the new air mass and its resulting physical properties affect air temperature and other meteorological elements of weather. Nonperiodic changes in weather also depend on ascending and descending air movements with accompanying adiabatic temperature changes that result in the development or decrease of cloudiness. The flow of cold, dry, and clear arctic air into Europe, for example, lowers the temperature, decreases the moisture content of the atmosphere, and increases visibility. Convection occurs when air is warmed by the earth. Cumulus clouds and brief showers result. The subsequent increasing pressure and descending air movements produce clear weather. In summer, this type of weather over a long period can lead to drought. In Europe, winter intrusions of air masses from the Atlantic cause mild overcast weather with resulting thaws and fog.

The nonperiodic changes in weather caused by the passage of atmospheric fronts, cyclones, and anticyclones are especially sharp. In zones where atmospheric fronts occur, ascending air movements form extensive cloud systems, which cause steady precipitation. In the tropics, cloud concentrations and abundant precipitation are caused by convection in the intertropical zone of air convergence, particularly during tropical cyclones, or hurricanes. The development and movement of cyclones and anticyclones move air masses considerable distances, which results in corresponding nonperiodic weather changes. These weather changes are caused by shifts in wind direction and velocity, with increasing or decreasing cloudiness. Other significant weather factors are small-scale vortices, such as waterspouts and tornadoes, and orographic air currents, such as foehns, boras, and drainage (for gravity) winds.

The intensity of nonperiodic changes in weather tends to diminish with altitude. However, even in the upper troposphere there are sharp intensifications of wind and turbulence due to jet streams. A record of jet streams is important for aviation.

Weather plays an important role in the economy and other aspects of man’s activity. This has resulted in the development of weather forecasting and the organization of a worldwide weather service to provide weather information and predictions.

REFERENCES

Khromov, S. P. Osnovy sinopticheskoi meteorologii. Leningrad, 1948.
Pogosian, Kh. P., and Z. L. Turketti. Atmosfera Zemli. Moscow, 1970.
Pogosian, Kh. P. Obshchaia tsirkuliatsiia atmosfery. Leningrad, 1972.
Sutton, O. G. Vyzov atmosfery. Leningrad, 1965. (Translated from English.)

S. P. KHROMOV

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Bibliography

weather

REFERENCES

Weather
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