Atmospheric Quirks--Oscillation of Equatorial Winds

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Atmospheric scientists think of the envelope of gases surrounding the earth as a sort of layer cake of four basic bands. The lowest is the troposphere, extending from sea level to about 5-10 miles above the earth. Next comes the stratosphere, which extends up to about 30 miles. It is in the stratosphere that the earth's protective ozone layer resides. Above the stratosphere lie the mesosphere and the thermosphere.

Two advances by UW atmospheric scientists during the 1960s relating to the earth's stratosphere have had a major impact on the field of atmospheric dynamics. In 1960, Richard Reed discovered an oscillation in the winds of the equatorial stratosphere, for which a theoretical interpretation was developed by James R. Holton in 1968.

This "quasi-biennial oscillation," as it is called, is a periodic variation in which the direction of the winds in the equatorial stratosphere changes between eastward and westward every 14 months. The oscillation occurs all along the equatorial zone.

Until the work of Holton and his colleague Richard S. Lindzen in 1968, no one had been able to account for the origin of this atmospheric quirk. Holton and colleagues showed that it is a natural internal oscillation resulting from interactions of prevailing winds with something called "buoyancy" waves. These are waves in the atmosphere generated by disturbances lower down in the atmospherein this case, convection over the tropics, where masses of air are heated and rise upward. The energy of the disturbance created by the rising air is propagated upward, through the upper layers above the rising air mass.

Holton and Lindzen's theory is responsible for a total shift in thinking about the circulation of air in the stratosphere. For the first time, it proved to the atmospheric sciences community that oscillating phenomena can arise from a complex interplay of natural, intrinsic processes in the atmosphere rather than having to be the direct function of an oscillation in external factors such as solar output or ocean temperature.

The UW work also has had a major impact on the study of variations in the ozone layer. Ozone depletion from the chemical reactions of chlorofluorocarbons with ozone has intensified over recent years. Ozone protects life on earth by filtering out harmful ultraviolet radiation that can damage DNA and cause skin cancer. The quasi-biennial oscillation plays an important role in the transport of ozone from equatorial regions, where the greatest amounts are generated, to higher latitutudes, where the ozone-depleting effects of chlorofluorocarbons are most severe.

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