عنوان مقاله [English]
نویسنده [English]چکیده [English]
In order to recognize and understand the mechanism governing on variations and decrease of
stratospheric ozone, the dynamical Principles which are governing on the stratosphere layer
were investigated. In this case, links between the most important dynamical components, i.e.
Polar Vortex, Planetary Scale Waves, Stratospheric Sudden Warming (SSW), QBO and
variations and depletion of stratospheric ozone, illustrated.
The results indicate that Stratospheric Polar Vortex has a key role in interannual
variability of Total ozone and account a necessary precondition for ozone depletion and
formation of stratospheric ozone hole. Therefore, Shape, Area, intensity and Persistence of
Polar Vortex in two hemisphere is determining ozone decrease rate and the maximum areal
coverage of ozone hole.
The results shows that dynamical forcing from troposphere is the major source of
stratospheric variations and upward propagation of planetary waves in addition to the
occurance Brewer-Dobson circulation and SSW, is controlling the temporal and spatial
distribution of total ozone and decrease and increase of stratospheric ozone. Hence, the
circulation of the winter stratosphere is strongly influenced by vertically propagating forced
planetary waves and rate of planetary waves activity in stratosphere and their interaction with
dynamical components such as QBO and Polar Vortex, additionally control of Brewer-
Dobson circulation and temperature ratio, is determining transport and interannual variability
of stratospheric ozone.
The Stratospheric Sudden Warming (SSW) is the most dramatic meteorological
phenomenon to take place in stratosphere. The breakup of the polar vortex during a major
SSW, or during a Final Warming, leads to the greatest mixing of polar and low-latitude air,
bringing, for instance, ozone-poor air from the polar vortex to mid-latitude.
The dominant source of variability in the tropical stratosphere is the QBO, which involves
the quasi-periodic reversal of zonal winds from westerly to easterly and back again. The results
shows that the zonal-wind structure in the stratosphere affects the propagation of planetary
waves from the troposphere. When the QBO is in its westerly phase throughout the tropical
lower stratosphere, the waves are refracted away from polar regions towards the tropics. The
stratosphere polar vortex should therefore be cold and strong, with less intense SSWs. When,
on the other hand, the QBO is in its easterly phase, the waves are more confined to middle and
polar latitudes. The polar vortex should be warmer and weaker and therefore more susceptible
to breakdown by SSWs. In such cases, ozone depletion is less in the Polar Regions and thus,
the ozone hole would be smaller.