Causes and Effects of Stratospheric Ozone Reduction An Update (1982) / Chapter Skim
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F DETECTION OF TRENDS IN THE VERTICAL DISTRIBUTION OF OZONE
F DETECTION OF TRENDS IN THE VERTICAL DISTRIBUTION OF OZONE
Pages 315-330
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From page 315... ...
The major uncertainties are due to changes in atmospheric concentrations of dust especially from volcanic eruptions, possible trends in cloudiness, and a serious problem of geographical representativeness. Global mean concentrations of ozone at particular altitudes are, however, rather meaningless since the vertical distribution of ozone varies markedly with latitude and season.
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From page 316... ...
. An ozone depletion of about 10 percent per decade should thus be detectable at the 95 percent confidence level in the middle stratosphere of the north temperate zone.
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From page 317... ...
However, individual sondes may differ in performance from the standard pressure-dependent correction factor, and subtle changes ; n the m~n~,facture or preparation of instruments could introduce a secular trend in this performance. Actual trends in ozone concentrations above balloon burst altitude can also cause fictitious trends in the profiles at lower altitudes to appear via the correction factor to the Dobson total amount (see Pittock 1977b)
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From page 318... ...
The vertical bars represent approximate 95 percent confidence intervals (Angell and Korshover 1981~.
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From page 319... ...
Thus an ozone change of about 11 percent per decade could be detected at the 95 percent confidence level. A change in ozone concentration at 30 km in the north temperate zone could be detected from the
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From page 320... ...
Trends in the ozone content of the upper troposphere are also of interest since the same theoretical models that predict ozone reduction in the middle and upper stratosphere predict ozone increases in the upper troposphere due to NOk emissions from the surface and/or aircraft exhausts. Estimates of revealed and unrevealed errors in trend determinations in the 2- to 8-km layer from ozonesonde data suggest that a change of about +18 percent at this level worldwide could be detected at the 9S percent confidence level (Hudson et al.
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From page 321... ...
in discussing total ozone measurements, the B W data from the NIMBUS-4 satellite, which commenced operation in April 1970, suffered from instrumental drift and also from a loss of spatial coverage after June 1972. Additional problems of spatial representativeness arose from interference with observations of vertical distributions caused by high-energy charged particles in the vicinity of the South Atlantic magnetic anomaly.
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From page 322... ...
The changing sensitivity of the NIMBUS-4 B W instrument has been taken into account by Heath using comparisons with near overpass Umkehr observations, assuming that the Umkehr network did not itself drift in calibration. The solar cycle effect was taken into account by assuming that natural concentrations of stratospheric ozone vary in phase with solar activity and that the amplitude of this effect increases monotonically with increasing altitude.
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From page 323... ...
Solid lines represent observed ozone variations. Dashed lines are assumed effect of solar cycle variations only.
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From page 324... ...
Nevertheless, it is clear from the error analysis of the NIMBUS-7 system that with only another 5 to 10 years of homogeneous wellcalibrated satellite data, and provided that the nature of the solar cycle effect at these altitudes can be more firmly established, it should be possible to determine whether or not significant reduction of ozone is occurring at these altitudes as current photochemical models suggest. The precise number of years of data needed to establish the existence of a statistically significant depletion within the range of theoretical possibilities will depend on the magnitude of the actual depletion and of the remaining uncertainties regarding the solar cycle effect.
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From page 325... ...
. CONCLUSI ONS Current observations of the vertical distribution of ozone are severely limited as tools for the detection of ozone depletion due to (a)
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From page 326... ...
Unless the solar cycle effect on ozone can be definitively described theoretically, it may be necessary to wait for accurate observations at critical altitudes over at least one whole solar cycle (11 years) in order to confidently infer that ozone depletion is due to pollution, even though the error limits in satellite vertical distribution measurements are small enough that a real trend in ozone concentration at 40-km altitude may be detected earlier.
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From page 327... ...
theoretical analysis of the solar cycle effects, (b) monitoring of solar ultraviolet radiation, solar protons, and any other solar outputs likely to affect ozone concentrations, and
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From page 328... ...
In view not only of the solar cycle effect, but also of the effect of changing temperature (due to increasing carbon dioxide concentrations) and variations in atmospheric circulation, other relevant meteorological variables and chemical constituents must be monitored in order both to test photochemical theory and reaction rates more critically and to enable a useful reduction in background variance due to causes other than pollution (e.g., see Bloomfield et al.
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From page 329... ...
Quarterly Journal of the Royal Meteorological Society 101:325-331. Dutsch, H.U.
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From page 330... ...
Quarterly Journal of the Royal Meteorological Society 96:32-39. Pittock, A.B.
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