The scientific study of global atmospheric processes: the receipt of solar radiation, evaporation, evapotranspiration, and precipitation, and the determination of, and changes in, atmospheric pressure (and, therefore, wind). Meteorology is generally concerned with the short-term processes (ie hours and days rather than months and seasons) operating in the troposphere and mesosphere, which are the atmospheric layers of the Earth's weather systems. Satellites are now the main source of meteorological data, the first purpose-built device being the American Tiros I, launched in 1960. The data are used for weather forecasting, and in meteorological and climatological research.
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. Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorologic oceanography studies interactions between our atmosphere and the ocean's hydrosphere.
The term meteorology comes from Aristotle's Meteorology (350 BC). Although the term meteorology is used today to describe a subdiscipline of the atmospheric sciences, Aristotle's work is more general. 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.
Blaise Pascal discovers in 1648 that atmospheric pressure decreases with height, and deduces that there is a vacuum above the atmosphere. Edmund Halley in 1686 maps the trade winds, deduces that atmospheric changes are driven by solar heat, and confirms the discoveries of Pascal about atmospheric pressure.
George Hadley in 1735 is the first to take the rotation of the Earth into account to explain the behavior of the trade winds. Understanding the kinematics of how exactly the rotation of the Earth affects airflow was partial at first. Benjamin Franklin (1743-1784) 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. Francis Beaufort in 1806 introduces his system for classifying wind speeds. In 1838 the controversial Law of Storms work by William Reid, which splits meteorological establishment into two camps in regard to low pressure systems.
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. 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. 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.
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. 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.
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.
In Bible times the forecasting of weather conditions was based solely upon observations of the sky. This is alluded to in the Bible book of Matthew where Jesus says to the religious leaders of the 1st Century, â€˜You are able to interpret the appearance of the sky but the sign of the times you cannot interpret.' This method of simple observation prevailed until 1643 when Italian physicist Evangelista Torricelli invented the barometer. This simple device was able to measure the pressure of the air. Torricelli noticed that air pressure changes in accordance with changes in the weather. In fact a drop in pressure would often signal that a storm was coming. Atmospheric humidity was also able to be measured when the hygrometer was invented in 1644. Then in 1714 German physicist Daniel Fahrenheit developed the mercury thermometer. It was now possible to accurately measure the weather.
It was in 1765 that daily measurements of air pressure, moisture content, wind speed and direction began to be made. This was first done by French scientist Laurent Lavoisier who stated,"With all of this information it is almost always possible to predict the weather one or two days ahead with reasonable accuracy." However things were not as simple as Lavoisier had thought. In 1854 a French warship and 38 merchant vessels sank in a fierce storm off the Crimean port of Balaklava. The director of the Paris Observatory was asked to investigate the disaster. On checking meteorological records it was seen that the storm had actually formed two days previous to the sinkings and had swept across Europe from the southeast. If a tracking system had been in place the ships could have been warned of the pending danger. As a result of these findings a national storm warning service was set up in France. This is recognized as the start of modern meteorology.
In the mid 1800s there was still no quick way of transferring weather data from one location to the next. Often the weather that was being warned about would arrive before the data did. That was until Samuel Morse invented his electric telegraph to allow speedy transference of information. Morse's invention now made it possible for the Paris Observatory to begin publishing the first modern weather maps. By 1872, Britain's Meteorological Office had followed suit. From then on the acquiring of weather data became more and more complex, as did the resulting meteorological maps. New graphic devices were developed to convey more information. Isobars, for example, were invented â€" lines drawn to link points that have the same barometric pressure. Isotherms connect locations that have the same temperature. Other graphic devices were also developed â€" symbols to show wind direction and force, as well as lines that depict the meeting of warm and cold air masses.
In the 20th century much sophisticated meteorological equipment has also been developed. Today, weather stations release balloons that carry what are called radiosondes. These are instruments that can measure atmospheric conditions and then radio the information back to the station. Of course, weather stations today also use radar. In 1960 the world's first weather satellite, TIROS 1 was sent into space equipped with a TV camera. Today, weather satellites orbit the earth from pole to pole. Geostationary satellites stay in a fixed position above the earth and constantly monitor one part of the globe.
The forecasting of the weather took a leap forward when, shortly after World War One, British meteorologist Lewis Richardson stated that since the atmosphere follows the laws of physics, it is possible to use mathematical calculations to predict future weather conditions. His formulas, however, were so complicated that the weather would be upon him before he could figure out what it would be. His calculations also only allowed for weather readings taken at six hourly intervals. However, with the advent of computers, it became possible to work out Richardson's lengthy calculations quickly. A complex numerical weather model was now established that incorporated all the known physical laws governing the weather. The equations are utilized in the following way: meteorologists divide the earth's surface into a grid with grid points spaced 80 kilometers apart. The atmosphere above each square is called a box and observations of atmospheric wind, air pressure, temperature and humidity are recorded at 20 different levels of altitude. A computer than analyzes the data received from the more than 3,500 observation stations around the world and produces a forecast of what the world's weather will be for the next 15 minutes. Then a forecast for the next 15 minutes is produced. Repeating this process a computer can produce a six day world forecast in just 15 minutes.
To achieve even greater accuracy the British Meteorological Office has what is called the Limited Area Model which covers just the North Atlantic and European sectors. It's grid points are spaced at intervals of just 50 kilometers. However, the formulas used and the results achieved are only approximate descriptions of the behavior of the atmosphere. To achieve more accuracy the skills of the weather forecaster must come into play. The forecaster must use his skills and experience to decide what value to place on the data he receives. As an example, when air cooled by the North Sea moves over the European land mass, a thin cloud layer often forms. Whether this cloud layer means rain is on the way in continental Europe the next day or whether it simply evaporates in the sun's heat depends on a temperature difference of only a few tenths of a degree. It is up to the forecaster to predict which will be the case.
So, how accurate is the weather forecast? Britain's Meteorlogical Office claims an 86 % accuracy for it's 24 hour forecasts. 5 day forecasts are at 80 % accuracy. Why aren't they more accurate? Well, weather systems are extremely complex. It is simply not possible to take into account all of the factors necessary to provide a foolproof forecast. And scientists still don't fully understand all of the forces of nature that shape the weather. Despite this, however, modern weather forecasting gets it right most of the time. So, it still pays to check out the forecast before heading off for a day in the sun.Written by Rose Potter - Â© 2002 Pagewise
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).
With the development of powerful new supercomputers like the Earth Simulator in Japan, mathematical modeling of the atmosphere can reach unprecedented accuracy. 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.
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