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NASA researchers using 22 years of satellite-derived data have confirmed
a theory that the strength of long waves, bands of atmospheric energy
that circle the Earth, regulate the temperatures in the upper atmosphere
of the Arctic, and play a role in controlling ozone losses in the
stratosphere. These findings will also help scientists predict
stratospheric ozone loss in the future.
These long waves affect the atmospheric circulation in the Arctic by
strengthening it and warming temperatures, or weakening it and cooling
temperatures. Colder temperatures cause polar clouds to form, which lead
to chemical reactions that affect the chemical form of chlorine in the
stratosphere. In certain chemical forms, chlorine can deplete the ozone
Just as the weather at the Earths surface varies a lot from one year to
the next, so can the weather in the stratosphere. For instance, there were some years, like 1984, in which it didnt get cold enough in the
Arctic stratosphere for significant ozone loss to occur. During that
year, we saw stronger and more frequent waves around the world that
acted as the fuel to a heat engine in the Arctic, and kept the polar
stratosphere from becoming cold enough for great ozone losses, said
Paul Newman, lead author of the study and an atmospheric scientist at
NASAs Goddard Space Flight Center, in Greenbelt, Md.
Other years, like 1997, weaker and less frequent waves reduced the
effectiveness of the Arctic heat engine and cooled the stratosphere,
making conditions just right for ozone destruction, Newman said. His
teams research appears in the September 16 issue of Journal of Geophysical
A long wave or planetary wave is like a band of energy, thousands of
miles in length that flows eastward in the middle latitudes of the upper
atmosphere, and circles the world. It resembles a series of ocean waves
with ridges (the high points) and troughs (the low points). Typically,
at any given time, there are between one and three of these waves
looping around the Earth.
These long waves move up from the lower atmosphere (troposphere) into
the stratosphere, where they dissipate. When these waves break up in the
upper atmosphere they produce a warming of the polar region. So, when
more waves are present to break apart, the stratosphere becomes warmer.
When fewer waves rise up and dissipate, the stratosphere cools, and more ozone loss occurs.
Weaker long waves over the course of the Northern Hemispheres winter
generate colder Arctic upper air temperatures during spring. By knowing
the cause of colder temperatures, scientists can better predict what
will happen to the ozone layer.
The images above show the relationship between atmospheric long waves in February of
1984 (left) and 1997 (right), and ozone. Color represents total ozone anomaly for the month of
Marchthe difference between the measured ozone and the March ozone levels
averaged over many years. In 1984, strong long waves warmed the Arctic
stratosphere, reducing the amount of ozone loss. In 1997, however, weak long
waves were not powerful enough to mix warm tropospheric air into the
stratosphere, resulting in greater than normal ozone loss.
Images courtesy Eric Nash and Paul Newman, NASA Goddard Space Flight Center.