Trends in Stratospheric

In short, the trends in the tropospheric concentrations of CFCs, halons, and their substitutes follow trends in their emissions. The effects of the controls imposed by the Montreal Protocol and its subsequent amendments are evident in the trends and have been used to show that the associated impact on ozone destruction is expected to begin about the turn of the century. The following section briefly describes the observed trends in stratospheric ozone. 

As discussed in Chapter 12, trends in stratospheric ozone in the Antarctic spring during formation of the ozone hole are clear. However, as treated in detail in 

Detecting and quantifying ozone trends in midlatitudes from anthropogenic perturbations is complex due to the effects of natural variations in stratospheric ozone and to the interactions between various effects (e.g., Krzyscin, 1994 Brasseur et al., 1995 Callis et al., 1997 Zerefos et al., 1997 Hood, 1997 Callis et al., 

long-term trends in ozone must be extracted from variability due to the solar cycle, which has an 11-year period associated with it, as well as the quasi-biennial cycle (QBO), which is an oscillation of zonal winds in the stratosphere around the equator and which has a 26-30 month cycle (e.g., see Kane et al., 

For example, Bjarnason et al. (1993) examined column 03 measurements made at Reykjavik from 1957 to 1990 using a Dobson spectrometer and applied a stratospheric model that included variations due to seasons, the solar cycle, the QBO, and a linear trend. The combination of the data and model showed a variation of 3.5 + 0.8% in column 03 over a solar cycle and 2.1 + 0.6% over a QBO, on top of a linear trend of decreasing 03. 

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Chandra, S and R. S. Stolarski, Recent Trends in Stratospheric Total Ozone Implications of Dynamical and El Chichon Perturbations, Geophys. Res. Lett., 18, 2277-2280 (f 99f). 

As discussed in more detail in this chapter, detecting trends in stratospheric ozone and deconvoluting the causes are complex, particularly outside the polar regions. However, it is estimated that for the Antarctic, where the most dramatic loss of ozone has been observed, recovery may be experimentally observable by the year 2008 if the Montreal Protocol and associated amendments are followed (e.g., Hofmann et al., 1994). 

At Arosa, Switzerland, where there are records back to 1926 (the longest data record available), the trend in annual mean 03 has been determined to be —(2.3 + 0.6)% per decade. When contributions due to the solar cycle, temperature, and stratospheric aerosol concentrations are taken into account, the trend is —(1.9 0.6)% per decade. However, the total measured column 03 includes both stratospheric and a smaller tropospheric contribution, and the latter has been increasing (see Chapters 14 and 16). This would tend to mask part of a decrease in stratospheric 03. Applying an estimate of the increase in tropospheric ozone gives a trend in stratospheric 03 of - (3.0 + 0.6)% per decade at Arosa (Staehelin et al., 1998b). 

Stolarski, R., R. Bojkov, L. Bishop, C. Zerefos, J. Staehelin, and J. Zawodny, Measured Trends in Stratospheric Ozone, Science, 256, 342-349 (1992). 

Stolarski.R.S., R.Bojkov, L.Bishop, C-Zerefos, J.Staehelin and J.Zawodny, (1992) Measured trends in stratospheric ozone, Science, 256,342-349... 

FIGURE 4-40 The Antarctic ozone hole, October 1991, as measured by the total ozone mapping spectrometer (TOMS) from the Nimbus 7 satellite. The hole covers the Antarctic continent and extends as far north as the tip of South America. (Reprinted with permission from R. Stolarski, R. Bojkov, L. Bishop, C. Zerefos, J. Staehelin, and J. Zawodny, 1992, Measured Trends in Stratospheric Ozone, Science 256 342-349. Copyright 1992, American Association for the Advancement of Science.)... 

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