Jet Stream

Introduction

Jet streams are relatively strong, fast-moving, but narrow (flat tube-shaped) currents of air located in the upper levels of the atmosphere. They are found both in the northern and southern hemispheres of planet Earth, but are less variable in the southern half. They range from 5 to 10 mi (8 to 16 km)—but average 7.5 mi (12 km)— above Earth's surface. This habitat is considered just under the boundary of the tropopause—the layer of atmosphere where weather occurs. Jet streams vary in altitude depending on the boundaries of warm and cold air. For instance, a frontal boundary is formed between cold polar air and warm tropical air, causing a strong polar jet stream.

The winds within a jet stream can top at 200 to 300 mi (320 to 480 km) per hour or higher but usually range around 50 to 60 mi (80 to 97 km) per hour. An average jet stream is thousands of miles long and hundreds of miles wide, but only a few miles thick. They generally travel from westerly to easterly directions, but sometimes detour in northern- and southern-directed loops.

Historical Background and Scientific Foundations

The swiftly flowing air currents, now called jet streams, that travel around Earth were first noticed in the 1800s by weather scientists experimenting with balloons and kites. They sometimes called these high winds “westerlies”: winds coming from the west. In the 1920s, Japanese meteorologist Wasaburo Ooishi used balloons to measure high winds over Mt. Fuji, just west of the country's capital of Tokyo. Other than inJapan, hisresearchonthe jetstreamfailedtobe recognized at that time by the world meteorological community.

American aviator Wiley Post (1898–1935) flew through some of these high winds in the late 1920s and early 1930s. On December 7, 1934, he discovered a strong wind that he used at around 20,000 ft (6,100m) to increase the speed of his airplane. Post is generally given credit for the discovery of the jet stream.

The jet stream was measured in great detail beginning in the early 1940s when radar was developed by engineers during World War II (1939–1945) and, concurrently, when weather radar first became available to scientists. The term RADAR was created in 1941 as an acronym for “radio detection and ranging.” Engineers found that when a transmitter emitted radio waves (a particular type of electromagnetic radiation), they could be reflected off a target and returned to a receiver, which was usually positioned with the transmitter. Objects could be detected and measured quite accurately with respect to their altitude, distance, and speed.

In the early twenty-first century, radar is used to detect precipitation (such as snow and rain) in meteorology, speeding motor vehicles (such as automobiles and motorcycles) in police traffic control, and enemy vessels (such as ships and aircraft) in the military.

Impacts and Issues

Differences in the jet stream can strongly affect the climate, especially in the Northern Hemisphere of Earth. A strong jet stream means that its winds are intense, regular, and compressed with its nominal path close to the pole. Because the jet stream, in this case, stays farther north, the warm climate at the equator is able to move farther northward, causing much warmer and temperate weather in these regions. Monsoon rains, for instance, can become more frequent and heavy, bringing flooding to affected areas such as those in southeastern Asia.

However, a weak jet stream contains highly variable and unpredictable winds that cause more irregularity in its path. The jet stream will oftentimes dip into the lower latitudes causing colder weather than normal. Snow in Houston, Texas, for instance, can result from a weak jet stream.

The jet stream also controls the movement of strong horizontal temperature and pressure gradients (contrasts, or differences, in temperature or pressure) such as weather fronts and high- and low-pressure weather systems. Jet streams often force large weather systems (such as hurricanes and rainstorms) to move in particular directions across the globe. For instance, a jet stream can move over the Gulf of Mexico and then turn north to drop large amounts of rainfall on the state of Texas and massive amounts of snowfall further northward on the Great Plains states of the United States.

WORDS TO KNOW

METEOROLOGY: The science that deals with Earth's atmosphere and its phenomena and with weather and weather forecasting.

MONSOON: An annual shift in the direction of the prevailing wind that brings on a rainy season and affects large parts of Asia and Africa.

RADAR: An acronym for RAdio Detection And Ranging—the use of electromagnetic waves at sub-optical frequencies (i.e., less than about 10¹² Hz) to sense objects at a distance.

RADIO WAVES: Electromagneticwavesthatoscillateorvibratebetween 3 and 300 billion times per second. Radio waves are physically identical to light waves, except that they do not vibrate as rapidly.

TROPOPAUSE: The boundary between the troposphere and the stratosphere (about 5 mi (8 km) in polar regions and about 9.3 mi (15 km) in tropical regions), usually characterized by an abrupt change of lapse rate. The regions above the troposphere have increased atmospheric stability than those below. The tropopause marks the vertical limit of most clouds and storms.

Thus, information collected about jet streams is important for the prediction of weather around the world and in the study of meteorology in general. Such weather forecasting uses numerical data of jet streams—their strength, location, altitude, and other physical characteristics—to develop complex systems of mathematical equations that are fed into supercomputers to produce scientific models of the atmosphere, and thus of global climate.

See Also Africa: Climate Change Impacts; Global Warming; Meteorology; Ocean Circulation and Currents;Oceans and Seas; Sea Temperatures and Storm Intensity.

BIBLIOGRAPHY

Books

Pernetta, John. Guide to the Oceans. Richmond Hill,Ontario, Canada: Firefly Books, 2003.

Voituriez, Bruno. The Changing Ocean: Its Effects on Climate and Living Resources. Paris, France: UNESCO, 2003.

Voituriez, Bruno. The Gulf Stream. Paris, France: UNESCO, 2006.

Wang, Chunzia, Shang-Ping Xie, and James A. Carton, eds. Earth's Climate: The Ocean-Atmosphere Interaction. Washington, DC: American Geophysical Union, 2004.

Web Sites

“Abrupt Climate Change: Should We Be Worried?” Woods Hole Oceanographic Institution. <http://www.whoi.edu/page.do?pid=12455&tid=282&cid=9986> (accessed October 27, 2007).