chapter 2 N92-15432 GLOBAL TRENDS Coordinator G. Mégie (France) Principal Authors M.-L. Chanin (France) J. C. Gille (USA) D. Ehhalt (FRG) M. P. McCormick (USA) P. Fraser (Australia) G. Mégie (France) J. F. Frederick (USA) M. Schoeberl (USA) Other Contributors L. Bishop (USA) J. B. Kerr (Canada) R. D. Bojkov (Switzerland) W. D. Komhyr (USA) W. Chu (USA) K. Kunzi (FRG) J. J. DeLuisi (USA) K. Labitzke (FRG) M. Geller (USA) C. Mateer (Canada) S. Godin (France) R. D. McPeters (USA) N. R. P. Harris (USA) A. J. Miller (USA) W. J. Hill (USA) R. M. Nagatani (USA) R. D. Hudson (USA) G. C. Reinsel (USA) G. C. Tiao (USA) /69 - CHAPTER 2 GLOBAL TRENDS TABLE OF CONTENTS 2.0 INTRODUCTION ..................................................................................163 2.1 OBSERVATIONAL METHODS RELEVANT TO TREND DETECTION ....................163 2.1.1 Introduction ................................................................................163 2.1.2 Measurements Used in Current Trend Analyses .........................................164 2.1.2.1 Total Ozone Measurements .....................................................164 2.1.2.2 Profile Measurements ............................................................168 2.1.3 Measurements for Future Trend Analyses ................................................174 2.1.3.1 Total Ozone Measurements ..................................................... 175 2.1.3.2 Profile Measurements ............................................................177 2.1.4 Comparisons of Errors/Capabilities .......................................................181 2.1.4.1 Intercompari sons Relevant to Present Data ....................................181 2.1.4.2 Intercompari sons Relevant to Future Trend Analyses .........................189 2.1.5 Temporal Sampling Requirements for Total Ozone Trend Detection ....................191 2.1.6 Concluding Remarks .......................................................................192 2.2 TRENDS IN TOTAL OZONE .....................................................................194 2.2.1 Introduction ................................................................................ 194 2.2.2 Trend Analysis of Dobson Total Ozone Data ............................................. 195 2.2.2.1 Result of the 1988 Ozone Trends Panel and Comparison with Other Studies ............................................................... 195 2.2.2.2 Sensitivity Analysis .............................................................. 204 2.2.2.3 Update of Trends into 1988 ...................................................... 207 2.2.2.4 Summary of Dobson Analyses and Comparison with Theory ................. 207 2.2.3 Analysis of Satellite-based Data from SBUV/TOMS Beginning in November 1978 210 2.2.3.1 Data Base and Analysis Procedure ............................................. 210 2.2.3.2 Geographic Patterns of Ozone Change and Comparison with the Dobson Network ....................................................... 214 2.2.3.3 Conclusion of Satellite Data Analyses .......................................... 219 2.3 TRENDS IN VERTICAL OZONE DISTRIBUTION ...........................................219 2.3.1 Introduction ................................................................................219 2.3.2 Comparison of SAGE I and SAGE II Stratospheric Ozone Measurements .............220 2.3.2.1 Zonal Means .....................................................................221 2.3.2.2 Change in SAGE I and SAGE 11 Ozone Concentrations ......................223 GLOBAL TRENDS 2.3.3 Analysis of Urnkehr Sonde Data ..........................................................226 2.3.4 Analysis of Ozonesonde Data .............................................................231 2.3.5 Comparisons with Model Calculations ....................................................234 2.4 TRENDS IN STRATOSPHERIC TEMPERATURE .............................................235 2.4.1 Introduction ................................................................................235 2.4.2 Stratospheric Temperature Data Sets .....................................................235 2.4.2.1 Radiosondes ......................................................................235 2.4.2.2 Rocketsondes ....................................................................236 2.4.2.3 Satellites ..........................................................................236 2.4.2.4 Lidar ..............................................................................236 2.4.3 Intercomparison of Stratospheric Temperature Data Sets ...............................237 2.4.3.1 Radiosonde, Rocketsonde, and Satellite Data ..................................237 2.4.3.2 Comparison of Lidar Data with SSU and NMC ................................237 2.4.4 Influence of Solar Activity .................................................................239 2.4.5 Updating of Previously Used Data Sets ...................................................240 2.4.6 Comparison with Trends in Ozone Distribution ..........................................243 2.5 TRENDS IN TROPOSPHERIC GASES AND OZONE .........................................244 2.5.1 Introduction ................................................................................244 2.5.2 Halocarbons ................................................................................245 2.5.2.1 CCI3F, CCl2172, CH3CCI3 , CCI4 ...................................................247 2.5.2.2 Other Chlorocarbons ............................................................247 2.5.2.3 Bromocarbons ...................................................................250 2.5.3 Nitrous Oxide ..............................................................................250 2.5.4 Methane .....................................................................................252 2.5.5 Carbon Monoxide ..........................................................................253 2.5.6 Carbon Dioxide .............................................................................256 2.5.7 Tropospheric Ozone ........................................................................257 2.6 TRENDS IN STRATOSPHERIC AEROSOLS ...................................................261 2.6.1 Introduction ................................................................................261 2.6.2 Stratospheric Aerosols .....................................................................261 2.6.3 Global Heterogeneous Effects .............................................................262 2.7 SURFACE ULTRAVIOLET RADIATION .......................................................263 2.7.1 Predicted Trends Related to Column Ozone, 1970-1986 ..................................263 2.7.2 Observed Trends in Surface Ultraviolet Radiation .......................................265 2.8 OUTSTANDING ISSUES .........................................................................267 APPENDIX2.A ...........................................................................................268 REFERENCES...........................................................................................271 GLOBAL TRENDS 2.0 INTRODUCTION Measuring trends in ozone, and most other geophysical variables, requires that a small systematic change with time be determined from signals that have large periodic and aperiodic variations. Their time scales range from the day-to-day changes due to atmospheric motions through seasonal and annual varia- tions to Il-year cycles resulting from changes in the sun ultraviolet output. Aperiodic variations include the irregular quasi-biennial oscillation, with a period of roughly 26-28 months, approximately 4-year variations, and other sources of interannual differences. Because the magnitude of all of these variations is not well known and highly variable, it is necessary to measure over more than one period of the variations to remove their effects. This means at least 2 or more times the 11 -year sunspot cycle. Thus, the first requirement is for a long-term data record. The second related requirement is that the record be consistent; a small effect is being sought, and changes in instru- mentation or data analysis method will obscure changes in the atmosphere. A third requirement is for reasonable global sampling, to ensure that the effects are representative of the entire Earth. Therefore, the various observational methods relevant to trend detection are reviewed in Section 2.1 to characterize their quality and time and space coverage. Available data are then examined for long-term trends or recent changes in ozone total content (Section 2.2) and vertical distribution (2.3), as well as in related parameters such as stratospheric temperature (2.4), source gases and tropospheric ozone (2.5), and aerosols (2.6). The relation between trends in total column ozone and variations observed in the solar ultraviolet radiation at the ground are discussed in Section 2.7, and outstanding issues in trends detection are emphasized in Section 2.8. 2.1 OBSERVATIONAL METHODS RELEVANT TO TREND DETECTION 2.1.1 Introduction This section briefly describes the measurement techniques that have been used in the past or are expected to be used in the future to quantitatively measure trends in total ozone or the ozone vertical distribution. More detailed descriptions of these techniques have been presented elsewhere, in the Ozone Trends Panel Report (WMO, 1989, hereafter denoted OTP) and in previous reports (WMO, 1986; NASA, 1988), earlier ozone assessments,