The term weather observation refers to all of the equipment and techniques used to study the properties of the atmosphere. These include such well-known instruments as the thermometer and barometer, as well as less familiar devices such as the radiosonde and devices for detecting the presence of trace gases in the atmosphere.
The fundamental principles on which the most common atmospheric observational instruments are based were discovered during the seventeenth and eighteenth centuries. For example, the Italian physicist Evangelista Torricelli (1608–1647) invented the first barometer in 1643, while the air hygrometer, a device for measuring atmospheric humidity, was invented by the Swiss physicist Horace Be´ne´dict de Saussure (1740–1799) in about 1780.
These instruments were useful at first in studying atmospheric properties close to the ground, but not at very high altitudes. In 1648, the French physicist Florin Pe´rier asked his brother-in-law to carry a pair of barometers to the top of Puy-de-Doôme to make measurements of air pressure there, but that was about the limit to which humans themselves could go.
One of the first means developed for raising scientific instruments to higher altitudes was the kite. In one of the most famous kite experiments of this kind, Benjamin Franklin used a kite in 1752 to discover that lightning was a form of electricity. Within a short period of time, kites were being used by other scientists to carry recording thermometers into the atmosphere, where they could read temperatures at various altitudes.
An important breakthrough in atmospheric observation came in the late eighteenth century with the invention of the hot-air balloon. Balloon flights made it possible to carry instruments thousands of feet into the atmosphere to take measurements. The English physician John Jeffries is often given credit for the first balloon ascension for the purpose of making meteorological measurements. In 1785 Jeffries carried a thermometer, barometer, and hygrometer to a height of 9,000 ft (2,700 m) in his balloon.
For the next 150 years, balloons were the primary means by which instruments were lifted into the atmosphere for purposes of observation. A number of devices were invented specifically for use in weather balloons. The most commonly used of these devices were the meteorograph and the radiosonde, both of which are combinations of instruments for measuring temperature, pressure, humidity, and other atmospheric properties.
The radiosonde differs from a meteorograph in that it also includes a radio that can transmit the data collected back to Earth. When the radiosonde is also used to collect data about atmospheric winds, it is then known as a rawinsonde. In most cases, data collected with the meteorograph is recovered only when the instrument is jettisoned from the balloon or airplane carrying it. At one time, scientists paid five dollars to anyone who found and returned one of these measuring devices.
Balloons are still an important way of transporting weather instruments into the atmosphere. Today, they are often very large pieces of equipment, made of very thin plastic materials and filled with helium gas. When the balloons are first released from the ground, they look as if they are nearly empty. However, as they rise into the atmosphere and the pressure around them decreases, they fill to their full capacity. Balloons used to study the properties of the upper atmosphere are known as sounding balloons.
The invention of the airplane and the rocket created new opportunities for the study of the atmosphere by making it possible to carry instruments far higher than they had ever gone before. At first, airplanes did similar work to that done by scientists traveling in balloons. Airplanes, however, performed that work much more efficiently, and at higher altitudes, with greater safety and comfort. As technology improved, aircraft began to take on new and more complex tasks. For example, they could fly through a cloud and collect cloud droplets on slides for future study. Today, airplanes are also used by so-called hurricane hunters, who fly into the middle of a hurricane to study its properties and movement.
Airplanes now used for atmospheric observation often have bizarre appearances. They may carry large platforms on their tops, oversized needles on their noses, or other attachments in which an array of observational instruments can be carried. One airplane used for atmospheric observation, a commercial DC8 aircraft, has been redesigned and outfitted to carry the equipment needed to measure levels of ozone and related chemicals over the Antarctic. Data collected from this airplane has been crucial in helping scientists understand how ozone levels have been decreasing over the South Pole over the past decade or more.
Unmanned rockets can carry measuring devices to altitudes even greater than is possible with a piloted aircraft. Again, rockets can perform the same standard measurements as a radiosonde, except at greater atmospheric heights. They can also perform more complex measurements. For example, they can be designed to carry and release a variety of chemicals that can then be tracked by radar and other systems located on the ground. Some rockets have also released explosive devices high in the atmosphere so that scientists can study the way in which sound waves are transported there.
The most sophisticated atmospheric observational systems of all are those that make use of artificial satellites. A weather satellite is a device that is lifted into Earth orbit by a rocket and that carries inside it a large number of instruments for measuring many properties of the atmosphere. The first weather satellite was put into orbit by the U.S. government on April 1, 1960. Its name was TIROS 1 (Television and Infrared Observation Satellite). Over the next five years, nine more satellites of the same name were launched. One of the primary functions of the TIROS satellites was to collect and transmit photographs of Earth’s cloud patterns.
In addition to the TIROS program, the U.S. government has put into operation a number of other weather satellite systems, including Nimbus, ESSA (Environmental Sciences Service Administration), and GOES (geosynchronous environmental satellites). The former Soviet Union also had an active program of weather observation by satellite. The first Soviet satellite was known as Kosmos 122, followed by a series of satellites known by the code name of Meteor. Following the launches by the United States and the former Soviet Union, Japan, the European Space Agency, India, and China have all launched weather satellites.
Satellites provide a variety of data about atmospheric properties that can contribute to improved weather forecasting. Satellites can track the development, growth, and movement of large storm systems, such as hurricanes and cyclones. This information can be used to warn of oncoming storms, save lives, and reduce property damage from severe storms.
Satellites can also take measurements using various wavelengths of light, thereby collecting data that would not be accessible to some other kinds of instruments. As an example, a satellite can photograph a cloud cover using both visible and infrared light and, by comparing the two, predict which cloud system is more likely to produce precipitation.
Meteorograph —An instrument designed to be sent into the atmosphere to record certain measurements, such as temperature and pressure.
Radiosonde —An instrument for collecting data in the atmosphere and then transmitting that data back to Earth by means of radio waves.
Rawinsonde —A type of radiosonde that is also capable of measuring wind patterns.
The observational systems described so far can be used to measure more than just physical properties such as temperature, pressure, and air movements. They can also be used to determine the chemical composition of the atmosphere. Such measurements can be valuable not only in the field of meteorology, but in other fields as well.
One of the earliest examples of such research dates to 1804, when the French physicist Joseph Louis Gay-Lussac traveled in a balloon to a height of 23,000 ft (6,900 m). At this altitude, he collected an air sample that he analyzed upon his return to the ground. Gay-Lussac found that the composition of air at 23,000 ft (6,900 m) was the same as it was at sea level.
An example of this kind of research today involves the issue of climate change. Over the past decade there has been a great deal of interest with respect to large scale changes in Earth’s climate. Many scientists believe that an accumulation of carbon dioxide and other gases in the atmosphere has been contributing to a gradual increase in Earth’s overall average annual temperature. This phenomenon is referred to as global warming. If such a change were, in fact, to occur, it would have significant effects on plant and animal (including human) life on Earth.
Many of the questions about global climate change cannot adequately be answered, however, without a fairly good understanding of the gases present in the atmosphere, changes in their concentration over time, and chemical reactions that occur among those gases. Until recently, most of those questions could not have been answered. Today, however, manned aircraft, rockets, and satellites are able to collect some of the kinds of data that will allow scientists to develop a better understanding of the chemical processes that occur in the atmosphere and the effects they may have on both weather and climate.
Ahrens, Donald C. Meteorology Today. Pacific Grove, Calif.: Brooks Cole, 2006.
David E. Newton