HISTORY OF METEOROLOGY •The scholars of ancient Greece were interested in the atmosphere and its related phenomena. About 340 bcGreek philosopher Aristotle wrote Meteorologica,a treatise on natural philosophy. His works, although speculative, represented the sum of knowledge about the natural science, including weather and climate. At that time, anything that fell from the sky (including rain and snow) and anything that was in the sky (including clouds) were called meteors, from the Greek word meteoros, meaning “high in the sky.” From meteoros comes the term meteorology. Several years later, Theophrastus, a pupil of Aristotle, compiled a book on weather forecasting, called the Book of Signs. His work consisted of ways to foretell the weather by noticing various weather-related indicators, such as a ring around the moon, which is often followed by rain. The work of Aristotle and Theophrastus remained a dominant influence in the study of weather and in weather forecasting for nearly 2000 years.
Although weather records were kept for different locations as early as the 14th century, meteorology did not become a genuine natural science until the invention of weather instruments. These instruments gave scientists data, so that the physical laws could be tested. Italian physicist and astronomer Galileo invented a crude thermometer in the late 1500s. Italian mathematician and physicist Evangelista Torricelli, a student of Galileo, invented the barometer in 1643. A few years later, French mathematician-philosophers Blaise Pascal and René Descartes, using a barometer, demonstrated that atmospheric pressure decreases with increasing altitude. In 1667 Robert Hooke, an English scientist, invented an anemometer for measuring wind speed. In 1714 German physicist Gabriel Daniel Fahrenheit worked on the boiling and freezing of water, and from that work he developed a temperature scale. In 1780 Horace de Saussure, a Swiss geologist and meteorologist, invented the hair hygrometer for measuring humidity.
The science of meteorology benefited from advances in other sciences, technology, and mathematics. In 1660 Irish-born English scientist Robert Boyle discovered the relationship between pressure and volume of a gas. English meteorologist George Hadley, in 1735, used physics and mathematics to explain how the earth’s rotation influences the trade winds in the tropics. By flying a kite in a thunderstorm in 1752, American statesman and scientist Benjamin Franklin demonstrated the electrical nature of lightning. French chemist Jacques Charles, in 1787, discovered the relationship between temperature and volume in a gas. In 1835 French physicist Gaspard de Coriolis mathematically demonstrated the effect that the earth’s rotation has on atmospheric motions.
The first system of classifying clouds was formulated by French botanist and zoologist Jean-Baptiste Lamarck in 1802. In 1803 Luke Howard, an English naturalist, devised a better system of classifying clouds. In 1806 British Admiral and hydrographer Francis Beaufort invented a wind scale for mariners. Enough weather information was available in 1821 that William Redfield, an American saddle maker and amateur meteorologist, was able to draw a crude weather map. By the 1840s ideas about winds and storms were partially understood. Meteorology got a giant boost in 1843 with the invention of the telegraph. Weather observations and information could now be rapidly disseminated.
A significant milestone in meteorology took place about 1920 when a group of Norwegian scientists, led by VilhelmBjerknes, and including Tor Bergeron, developed a model explaining the life cycle of a middle latitude storm system. These ideas were expanded as upper air observations became available from aircraft and radiosondes. By 1940 upper-level measurements of temperature, pressure, humidity, and wind gave atmospheric scientists a three-dimensional view of the atmosphere.
Weather radar became available to scientists during the early 1940s. At the same time, high-flying military aircraft discovered the existence of jet streams—swiftly flowing air currents that girdle the earth. In 1946 American chemist and Nobel laureate Irving Langmuir and American atmospheric physicist Vincent Schaefer found that tiny pellets of dry ice could induce supercooled liquid water droplets to crystallize. During the same year, Bernard Vonnegut, an American chemist, discovered that silver iodide crystals could cause these same water droplets to freeze. These events ushered in an active period of cloud seeding.
The atmospheric sciences advanced again in the 1950s when high-speed computers were able to solve the mathematical equations that describe the behavior of the atmosphere. Today, computers not only plot the observations and draw the lines on surface and upper-level maps, but they also predict the state of the atmosphere up to five days into the future.
In 1960 the National Aeronautics and Space Administration (NASA) launched Tiros 1, the first weather satellite. Subsequent satellites have been more sophisticated and have been capable of monitoring more aspects of the atmosphere. In the mid-1990s, the National Weather Service upgraded its conventional radar with a network of 135 Doppler radar units that are capable of peering into severe thunderstorms, unveiling hail, tornadoes, and strong winds.
INVENTION OF WEATHER INSTRUMENTS Anemometer (Greek anemos, “wind”; metron, “measure”), an instrument that measures wind speed. The most common kind of anemometer consists of three or four cups attached to short rods that are connected at right angles to a vertical shaft. As the wind blows, it pushes the cups, which turn the shaft. The number of turns per minute is translated into wind speed by a system of gears similar to the speedometer of an automobile. Wind velocity is also measured by the pressure of the air blowing into a Pitot tube (an L-shaped tube, one end open toward the flow of air and the other end connected to a pressure-measuring device), and electrically by the cooling effect of the wind on a heated wire, which causes the electric resistance of the wire to change.
Barometer, instrument for measuring atmospheric pressure, that is, the force exerted on a surface of unit area by the weight of the atmosphere. Because this force is transmitted equally in all directions through any fluid, it is most easily measured by observing the height of a column of liquid that, by its weight, exactly balances the weight of the atmosphere. A water barometer is far too large to be used conveniently. Liquid mercury, however, is 13.6 times as heavy as water, and the column of mercury sustained by normal atmospheric pressure is only about 760 mm (about 30 in) high.
Radiosonde, in meteorology, a radio-transmitting instrumented package carried into the atmosphere by balloon. The use of such probes in meteorology began following World War I but was not practiced on a regular basis until the late 1930s. Radiosondes are a major source of weather information, and are also useful for atmospheric and other research. They typically carry aloft a compact combination of temperature, pressure, and humidity sensors. The balloon movements also indicate wind direction at various heights. The ceiling for the use of radiosondes is about 30,000 m (about 100,000 ft), but balloons can be designed to go much higher.
Thermometer, instrument used to measure temperature. The most commonly used thermometer is the mercury-in-glass type, which consists of a uniform-diameter glass capillary that opens into a mercury-filled bulb at one end. The assembly is sealed to preserve a partial vacuum in the capillary. If the temperature increases, the mercury expands and rises in the capillary. The temperature may then be read on an adjacent scale. Mercury is widely used for measuring ordinary temperatures; alcohol, ether, and other liquids are also employed for this purpose.