Dynamic Analysis of the Role of Stratospheric Large Scale Circulation on the Stratospheric Ozone Depletion, Part II; Dynamical Mechanisms
Subject Areas : Geopolitic
عباس Mofidi
1
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ندارد
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Keywords: Stratosphere, Planetary Scale Waves, Polar Vortex, Quasi-Biennial Oscillation, Tropopause, Stratospheric Sudden Warming, Ozone Hole,
Abstract :
In order to recognize and understand the mechanism governing on variations and decrease ofstratospheric ozone, the dynamical Principles which are governing on the stratosphere layerwere investigated. In this case, links between the most important dynamical components, i.e.Polar Vortex, Planetary Scale Waves, Stratospheric Sudden Warming (SSW), QBO andvariations and depletion of stratospheric ozone, illustrated.The results indicate that Stratospheric Polar Vortex has a key role in interannualvariability of Total ozone and account a necessary precondition for ozone depletion andformation of stratospheric ozone hole. Therefore, Shape, Area, intensity and Persistence ofPolar Vortex in two hemisphere is determining ozone decrease rate and the maximum arealcoverage of ozone hole.The results shows that dynamical forcing from troposphere is the major source ofstratospheric variations and upward propagation of planetary waves in addition to theoccurance Brewer-Dobson circulation and SSW, is controlling the temporal and spatialdistribution of total ozone and decrease and increase of stratospheric ozone. Hence, thecirculation of the winter stratosphere is strongly influenced by vertically propagating forcedplanetary waves and rate of planetary waves activity in stratosphere and their interaction withdynamical components such as QBO and Polar Vortex, additionally control of Brewer-Dobson circulation and temperature ratio, is determining transport and interannual variabilityof stratospheric ozone.The Stratospheric Sudden Warming (SSW) is the most dramatic meteorologicalphenomenon to take place in stratosphere. The breakup of the polar vortex during a majorSSW, 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 involvesthe quasi-periodic reversal of zonal winds from westerly to easterly and back again. The resultsshows that the zonal-wind structure in the stratosphere affects the propagation of planetarywaves from the troposphere. When the QBO is in its westerly phase throughout the tropicallower stratosphere, the waves are refracted away from polar regions towards the tropics. Thestratosphere 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 andpolar latitudes. The polar vortex should be warmer and weaker and therefore more susceptibleto breakdown by SSWs. In such cases, ozone depletion is less in the Polar Regions and thus,the ozone hole would be smaller.
