J11.5
The role of mid-latitude planetary waves in predicting the severity of Antarctic ozone depletion
Petra E. Huck, Univ. of Canterbury, Christchurch, New Zealand; and A. J. McDonald and G. Bodeker
Previous analyses based on measurements1 and modelling2,3 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 reactions5,6.
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.
References 1. Bodeker, G.E., and M.W.J. Scourfield, Planetary waves in total ozone and their relation to Antarctic ozone depletion, Geophysical Research Letters, 22 (21), 2949 - 2952, 1995. 2. Shindell, D.T., S. Wong, and D. Rind, Interannual variability of the Antarctic ozone hole in a GCM. Part I: the influence of tropospheric wave variability, Journal of the Atmospheric Sciences, 54, 2308-2319, 1997. 3. Shindell, D.T., D. Rind, and N. Balachandran, Interannual variability of the Antarctic ozone hole in a GCM. Part II: a comparison of unforced and QBO-induced variability, Journal of the Atmospheric Sciences, 56, 1873-1874, 1999. 4. Hanson, D., and K. Mauersberger, Laboratory studies of the nitric acid trihydrate: Implications for the South Polar Stratosphere, Geophysical Research Letters, 15 (8), 855-858, 1988. 5. Solomon, S., J.P. Smith, R.W. Sanders, L. Perliski, H.L. Miller, G.H. Mount, J.G. Keys, and A.L. Schmeltekopf, Visible and Near-Ultraviolet Spectroscopy at McMurdo Station, Antarctica 8. Observations of Nighttime NO2 and NO3 From April to October 1991, Journal of Geophysical Research, 98 (D1), 993-1000, 1993. 6. Roscoe, H.K., A.E. Jones, and A.M. Lee, Midwinter start to Antarctic ozone depletion: evidence from observations and models, Science, 278, 93-96, 1997.
.Joint Session 11, stratosphere chemistry/radiation/climate feedback processes (Joint with Middle Atmosphere, Fluid Dynamics and Climate Variations)
Friday, 17 June 2005, 10:30 AM-1:15 PM, Ballroom D
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