The role of mid-latitude planetary waves in predicting the severity of Antarctic ozone depletion

Previous analyses based on measurements¹ and modelling^2,3 have shown that inter-annual differences in the severity of Antarctic ozone depletion are anticorrelated with the southern hemisphere mid-latitude planetary wave activity. This study updates the earlier analysis to provide a revised estimate of the extent to which mid-latitude planetary waves, and polar temperatures, control the severity of Antarctic ozone depletion.

The mechanisms which link planetary wave activity to Antarctic ozone depletion processes occur throughout the Antarctic vortex period. Models suggest that the most important mechanism is through planetary wave modulation of vortex temperatures and that midwinter tropospheric wave energy may be a good predictor of the severity of the Antarctic ozone hole the following spring². The primary purpose of this paper is to use observations to examine in greater detail how planetary wave activity and the severity of Antarctic ozone depletion are coupled over the course of a season (June to December). The rate at which ozone is depleted within the vortex depends on ClO and BrO concentrations which are in turn dependent on:

i) Total halogen loading in the stratosphere, in our study quantified using effective equivalent stratospheric chlorine (EESC).

ii) Activation of halogen containing molecules to more active forms on the surfaces of polar stratospheric clouds (PSCs). The volume of PSCs within the vortex is a function of HNO₃ and H₂O concentrations and polar temperatures⁴ (which are affected by planetary waves).

iii) Photolysis of Cl₂O₂ to form ClO, the rate limiting step in the ozone destruction cycle. Early in the season, distortion of the vortex by planetary waves may expose air that would otherwise remain in polar darkness to sunlight, thereby stimulating an early start to ozone depletion reactions^5,6.

These drivers of Antarctic ozone depletion are combined in a simple mechanistic model to examine on a day by day basis the extent to which planetary wave activity early in the season (June, July and August) may be used to predict the severity of Antarctic ozone depletion late in the season (October and November). In addition ozone loss rates within the vortex over the season are examined as a function of these drivers.

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