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Meteorology

2007 Schools Wikipedia Selection. Related subjects: Climate and the Weather

                         Atmospheric sciences [cat.]
                                                 Meteorology [cat.]

           weather [cat.]
           tropical cyclones [cat.]

                                                 Climatology [cat.]

           climate [cat.]
           climate change [cat.]
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             Portal Atmospheric Sciences
             Portal Weather

   Satellite image of Hurricane Hugo with a polar low visible at the top
   of the image.
   Enlarge
   Satellite image of Hurricane Hugo with a polar low visible at the top
   of the image.
   Aristotle
   Enlarge
   Aristotle

   Meteorology is the interdisciplinary scientific study of the atmosphere
   that focuses on weather processes and forecasting. Meteorological
   phenomena are observable weather events which illuminate and are
   explained by the science of meteorology. Those events are bound by the
   variables that exist in Earth's atmosphere. They are temperature,
   pressure, water vapor, and the gradients and interactions of each
   variable, and how they change in time. The majority of Earth's observed
   weather is located in the troposphere.

   Meteorology, climatology, atmospheric physics, and atmospheric
   chemistry are sub-disciplines of the atmospheric sciences. Meteorology
   and hydrology comprise the interdiscplinary field of hydrometeorology.

   Interactions between our atmosphere and the oceans are part of coupled
   ocean-atmosphere studies. Meteorology has application in many diverse
   fields such as the military, energy production, farming, shipping and
   construction.

History of meteorology

Early achievements in meteorology

     * 350 BC

   The term meteorology comes from Aristotle's Meteorology.

   Although the term meteorology is used today to describe a subdiscipline
   of the atmospheric sciences, Aristotle's work is more general. The work
   touches upon much of what is known as the earth sciences. In his own
   words:

     ...all the affections we may call common to air and water, and the
     kinds and parts of the earth and the affections of its parts.

   One of the most impressive achievements in Meteorology is his
   description of what is now known as the hydrologic cycle:

     Now the sun, moving as it does, sets up processes of change and
     becoming and decay, and by its agency the finest and sweetest water
     is every day carried up and is dissolved into vapour and rises to
     the upper region, where it is condensed again by the cold and so
     returns to the earth.

     * 1607

   Galileo Galilei constructs a thermoscope. Not only did this device
   measure temperature, but it represented a paradigm shift. Up to this
   point, heat and cold were believed to be qualities of Aristotle's
   elements (fire, water, air, and earth). Note: There is some controversy
   about who actually built this first thermoscope. There is some evidence
   for this device being independently built at several different times.
   This is the era of the first recorded meteorological observations. As
   there was no standard measurement, they were of little use until the
   work of Daniel Gabriel Fahrenheit and Anders Celsius in the 18th
   century.
     * 1643

   Evangelista Torricelli, a contemporary and one-time assistant of
   Galileo, creates the first man-made sustained vacuum in 1643, and in
   the process creates the first barometer. Changes in height of mercury
   in this Toricelli Tube lead to his discovery that atmospheric pressure
   changes over time.
     * 1648

   Blaise Pascal discovers that atmospheric pressure decreases with
   height, and deduces that there is a vacuum above the atmosphere.
     * 1667

   Robert Hooke builds an anemometer to measure windspeed.
     * 1686

   Edmund Halley maps the trade winds, deduces that atmospheric changes
   are driven by solar heat, and confirms the discoveries of Pascal about
   atmospheric pressure.
     * 1735

   George Hadley is the first to take the rotation of the Earth into
   account to explain the behaviour of the trade winds. Although the
   mechanism Hadley described was incorrect, predicting trade winds half
   as strong as the actual winds, the circulating cells that Hadley
   described later become known as Hadley cells.
   Benjamin Franklin
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   Benjamin Franklin
     * 1743- 1784

   Benjamin Franklin observes that weather systems in North America move
   from west to east, demonstrates that lightning is electricity,
   publishes the first scientific chart of the Gulf Stream, links a
   volcanic eruption to weather, and speculates about the effect of
   deforestation on climate.
     * 1780

   Horace de Saussure constructs a hair hygrometer to measure humidity.
     * 1802- 1803

   Luke Howard writes On the Modification of Clouds in which he assigns
   cloud types Latin names.
     * 1806

   Francis Beaufort introduces his system for classifying wind speeds.
     * 1838

   Controversial Law of Storms work by William Reid , which splits
   meteorological establishment into two camps in regard to low pressure
   systems. It would take over ten years of debate to finally come to a
   consensus on the behaviour of low pressure systems.
     * 1841

   Elias Loomis the first person known to attempt to devise a theory on
   frontal zones. This idea did not catch on until expanded upon by the
   Norwegians in the years following World War I.

Observation networks and weather forecasting

   The arrival of the electrical telegraph in 1837 afforded, for the first
   time, a practical method for gathering quickly information on surface
   weather conditions from over a wide area. These data could be used to
   produce maps of the state of the atmosphere for a region near the
   Earth's surface and to study how these states evolved through time. To
   make frequent weather forecasts based on these data required a reliable
   network of observations, but it was not until 1849 that Smithsonian
   Institute began to establish an observation network across the United
   States under the leadership of Joseph Henry . Similar observation
   networks were established in Europe at this time. In 1854, the United
   Kingdom gorvernment appointed Robert FitzRoy to the new office of
   Meteorological Statist to the Board of Trade with the role of gathering
   weather observations at sea. FitzRoy's office become the United Kingdom
   Meteorological Office in 1854, the first national meteorological
   service in the world. The first daily weather forecasts made by
   FitzRoy's Office were published in The Times newspaper in 1860. The
   following year a system was introduced of hoisting storm warning cones
   at principal ports when a gale was expected.

   Over the next 50 years many countries established national
   meteorological services: Finnish Meteorological Central Office (1881)
   was formed from part of Magnetic Observatory of Helsinki University;
   India Meteorological Department (1889) established following tropical
   cyclone and monsoon related famines in the previous decades; United
   States Weather Bureau (1890) was established under the Department of
   Agriculture; Australian Bureau of Meteorology (1905) established by a
   Meteorology Act to unify existing state meteorological services.

The Coriolis effect

   Understanding the kinematics of how exactly the rotation of the Earth
   affects airflow was partial at first. Late in the 19th century the full
   extent of the large scale interaction of pressure gradient force and
   deflecting force that in the end causes air masses to move along
   isobars was understood. Early in the 20th century this deflecting force
   was named the Coriolis effect after Gaspard-Gustave Coriolis, who had
   published in 1835 on the energy yield of machines with rotating parts,
   such as waterwheels. In 1856, William Ferrel proposed the existence of
   a circulation cell in the mid-latitudes with air being deflected by the
   coriolis force to create the prevailing westerly winds.

Numerical weather prediction

   A meteorologist at the console of the IBM 7090 in the Joint Numerical
   Weather Prediction Unit. c. 1965
   Enlarge
   A meteorologist at the console of the IBM 7090 in the Joint Numerical
   Weather Prediction Unit. c. 1965

   In 1904 the Norwegian scientist Vilhelm Bjerknes first postulated that
   prognostication of the weather is possible from calculation based upon
   natural laws.

   Early in the 20th century, advances in the understanding of atmospheric
   physics led to the foundation of modern numerical weather prediction.
   In 1922, Lewis Fry Richardson published `Weather prediction by
   numerical process` which described how small terms in the fluid
   dynamics equations governing atmospheric flow could be neglected to
   allow numerical solutions to be found. However, the sheer number of
   calculations required was too large to be completed before the advent
   of computers.

   At this time in Norway a group of meteorologists led by Vilhelm
   Bjerknes developed the model that explains the generation,
   intensification and ultimate decay (the life cycle) of mid-latitude
   cyclones, introducing the idea of fronts, that is, sharply defined
   boundaries between air masses. The group included Carl-Gustaf Rossby
   (who was the first to explain the large scale atmospheric flow in terms
   of fluid dynamics), Tor Bergeron (who first determined the mechanism by
   which rain forms) and Jacob Bjerknes.

   Starting in the 1950s, numerical experiments with computers became
   feasible. The first weather forecasts derived this way used barotropic
   (that means, single-vertical-level) models, and could successfully
   predict the large-scale movement of midlatitude Rossby waves, that is,
   the pattern of atmospheric lows and highs.

   In the 1960s, the chaotic nature of the atmosphere was first observed
   and understood by Edward Lorenz, founding the field of chaos theory.
   These advances have led to the current use of ensemble forecasting in
   most major forecasting centers, to take into account uncertainty
   arising due to the chaotic nature of the atmosphere.

Satellite observation

   In 1960, the launch of TIROS-1, the first successful weather satellite
   marked the beginning of the age where weather information is available
   globally. Weather satellites along with more general-purpose
   Earth-observing satellites circling the earth at various altitudes have
   become an indispensable tool for studying a wide range of phenomena
   from forest fires to El Niño.

   In recent years, climate models have been developed that feature a
   resolution comparable to older weather prediction models. These climate
   models are used to investigate long-term climate shifts, such as what
   effects might be caused by human emission of greenhouse gases.

Weather forecasting

   A meteorogist at work at the Storm Prediction Center in Norman, OK.
   Enlarge
   A meteorogist at work at the Storm Prediction Centre in Norman, OK.

   Although meteorologists now rely heavily on computer models (numerical
   weather prediction), it is still relatively common to use techniques
   and conceptual models that were developed before computers were
   powerful enough to make predictions accurately or efficiently
   (generally speaking, prior to around 1980). Many of these methods are
   used to determine how much skill a forecaster has added to the forecast
   (for example, how much better than persistence or climatology did the
   forecast do?). Similarly, they could also be used to determine how much
   skill the industry as a whole has gained with emerging technologies and
   techniques.
     * Persistence method

   The persistence method assumes that conditions will not change. Often
   summarised as "Tomorrow equals today". This method works best over
   short periods of time in stagnant weather regimes.
     * Extrapolation method

   This assumes that the systems in the atmosphere propogate at similar
   speeds than seen in the past at some distance into the future. This
   method works best over short periods of time, and works best if you
   take diurnal changes in the pressure and precipitation patterns into
   account.
     * Numerical forecasting method

   The numerical weather prediction or NWP method uses computers to take
   into account a large number of variables and creates a computer model
   of the atmosphere. This is most successful when used with the methods
   below, and when model biases and relative skill are taken into account.
   In general, the ECMWF model outperforms the NCEP ensemble mean, which
   outperforms the UKMET/GFS model after 72 hours, which outperform in the
   NAM model at most time frames. This performance changes when tropical
   cyclones are taken into account, as the ECMWF/model ensemble
   methods/model consensus/GFS/UKMET/NOGAPS/ all perform exceedingly well,
   with the NAM and Canadian GEM exhibiting lower accuracy.
     * Consensus/ensemble methods of forecasting

   Statistically, it is difficult to beat the mean solution, and the
   consensus and ensemble methods of forecasting take advantage of the
   situation by only favoring models that have the greatest support with
   their ensemble means or other pieces of global model guidance. A local
   Hydrometeorological Prediction Centre study showed that using this
   method alone verifies 50-55% of the time.
     * Trends method

   The trends method involves determining the change in fronts and high
   and low pressure centers in the model runs over various lengths of
   time. If the trend is seen over a long enough time frame (24 hours or
   so), it is more meaningful. The forecast models have been known to
   overtrend however, so use of this method verifies 55-60% the time, more
   so in the surface pattern than aloft.
     * Climatology/Analog method

   The 'climatology or analog method involves using historical weather
   data collected over long periods of time (years) to predict conditions
   on a given date. A variation on this theme is the use of
   teleconnections, which rely upon the date and the expected position of
   other positive or negative 500 hPa height anomalies to give someone an
   impression of what the overall pattern would look like with this
   anomaly in place, and is of more significant help than a model trend
   since it verifies roughly 75 percent of the time, when used properly
   and with a stable anomaly centre. Another variation is the use of
   standard deviations from climatology in various meteorological fields.
   Once the pattern deviates more than 4-5 sigmas from climatology, it
   becomes an improbable solution.

Meteorology and climatology

   With the development of powerful new supercomputers like the Earth
   Simulator in Japan, mathematical modeling of the atmosphere can reach
   unprecedented accuracy. This is not only due to the enhanced spatial
   and temporal resolution of the grids employed, but also because these
   more powerful machines can model the Earth as an integrated climate
   system, where atmosphere, ocean, vegetation, and man-made influences
   depend on each other realistically. The goal in global meteorological
   modeling can be termed Earth System Modeling, with a growing number of
   models of various processes coupled to each other. Predictions for
   global effects like Global Warming and El Niño are expected to benefit
   substantially from these advancements.

   Regional models are attracting more interest as the resolution of
   global models increases. With regional weather disasters such as the
   Elbe flooding in 2002 and the European heat wave in 2003, decision
   makers expect from these models accurate assessments about the possible
   increase of these natural hazards in a specific region. Countermeasures
   such as dikes or intentional flooding might be effective in preventing
   or at least attenuating natural hazards.

   For models at all scales, increased model resolution means less
   reliance on parameterizations, which are empirically derived
   expressions for processes that cannot be resolved on the model grid.
   For example, in mesoscale models individual clouds can now be resolved,
   removing the need for formulations that average over a grid box. In
   global modeling, atmospheric waves such as gravity waves with short
   temporal and spatial scales can be represented without resorting to
   often overly simplified parameterizations.

   Retrieved from " http://en.wikipedia.org/wiki/Meteorology"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
