WORLD METEOROLOGICAL ORGANIZATION

UNITED NATIONS ENVIRONMENT PROGRAMME

AUSTRALIA

Prepared by the Atmosphere Watch Section, Bureau of Meteorology

MONITORING

The Bureau of Meteorology Ozone Monitoring Unit uses Dobson spectrophotometers to monitor total column ozone at six stations in Australia: Melbourne, Perth, Brisbane, Macquarie Island, Darwin and Hobart (under repair at present). On average, each station takes up to six observations per day. These instruments are used to make Umkehr observations to estimate the vertical profile of ozone in the stratosphere. The automatic Dobson at Perth airport can do two Umkehr observations per day. One Umkehr observation per week is taken at stations other than Macquarie Island (where the climate does permit it). To make measurements of the atmospheric profile of ozone, one ozone sonde per week is released from Melbourne. During 1994, the Bureau, with support from the Cooperative Research Centre for Southern Hemisphere Meteorology (CRC-SHM) and the Australian Government's Environment Protection Agency, conducted a programme of ozone sonde releases at Macquarie Island in support of the Airborne Southern Hemisphere Ozone Experiment (ASHOE). Data are checked and coded to the WMO World Ozone and UV Data Centre (WOUDC) standards for archival and international perusal three to four months after collection. Monitoring of ozone depleting substances is conducted at the Cape Grim Baseline Air Pollution Station (CGBAPS).

RESEARCH

Research within the Bureau of Meteorology, using the Macquarie Island total ozone, stratospheric wind and temperature data set has been used to explain the ozone variations during 1969-90 in terms of atmospheric dynamics. Statistical analyses are being carried out on data from the satellite borne Backscattered Ultra Violet (BUV), Solar Backscatter Ultra Violet (SBUV) and Stratospheric Aerosol Gas Experiment (SAGE) instruments in order to ascertain the altitude distribution of winter ozone reductions. The large amount of data collected from the Australian ozone monitoring network provides an opportunity for the analysis of trends and for the development of methods of quality control for contemporary data. Using statistical methods it has been possible to analyse significant trends in the Australian data.

The CRC-SHM is developing a three dimensional (3-D) ozone data assimilation and analysis system. It is being tested using data from research satellites and ASHOE observations for the October 1994 period. It will also be used for operational ozone analysis and short- term forecasts of the 3-D ozone distribution for use in ultra violet (UV) radiation forecasts (see below). The 3-D ozone analyses will be used to investigate stratospheric transport processes, such as ozone transport accompanying polar vortex breakdown, and to initialise the CRC-SHM chemical transport model (CTM).

Multi-year calculations of long-lived tracers will be used to infer the relative roles of residual advection and quasi-horizontal mixing in determining the distribution of trace gases, and also to examine the transport and mixing between various regions of the stratosphere. These transport and mixing processes will be further examined using calculations with the CTM and trajectory codes. Results will help interpret measurements from aircraft and satellites. Simulations of the evolution of ozone during the austral winter for periods of 1 to 2 months will be performed using analysed winds, and using different degrees of parametrisation of the chemical processes which lead to production and subsequent loss of ozone. Studies will extend to examination of: the 3-D characteristics of filaments of polar air; the dynamics of vortex break-up and accompanying mixing; upper tropospheric dynamics and stratosphere-troposphere interchange and; gravity wave processes.

The modulation of the UV-B fluxes in the atmosphere arising from transport and chemical modulation of the ozone content on the lower stratosphere are significant environmental issues in the southern hemisphere and a high spectral resolution UV radiative transfer model will be used with the ozone analyses and forecasts described earlier to provide analyses and forecasts of surface UV-B radiation dosage. These will be verified against measurements from the Bureau's radiation network and the Australian Radiation Laboratory and compared with UV-B prediction schemes being developed overseas.

The CRC-SHM participated in ASHOE/Measurements for Assessing the Effects of Stratospheric Aircraft (MAESA) mission in 1994, the Stratospheric Tracers of Atmospheric Transport (STRAT) in 1995 (and 1996), collaborative projects with the US National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL) and the Massachusetts Institute of Technology (MIT) Dynamical Theory group. The NOAA/CRC-SHM project involved the measurement of those trace species defining the total chlorine budget before, during and after the formation of the Antarctic ozone hole. The CRC-SHM/MIT Theory team's activities were concerned with examining the nature of trace gas transport in the lower stratosphere, and with assessing the ability of operational meteorological analysis and prediction schemes to represent the observed stratospheric meteorology and trace gas distribution. Further international collaboration is occurring with the NASA STRAT airborne observation programme, and with a number of stratospheric research centres in the United States and England.

At CGBAPS, observations of ozone depleting substances (chlorofluorocarbons (CFCs), methyl chloroform, carbon tetrachloride, nitrous oxide) are the longest continuous real time records in the world. The Ozone Depletion Potential (ODP) of these depends on assumptions made about their atmospheric lifetimes. Data collected at CGBAPS and other global background sites have been used to provide independent estimates on lifetimes (and hence ODPs).

Methyl chloroform data from CGBAPS and other global sites have been used to determine the global abundance of the hydroxyl radical, which affects the ODP calculations of all ozone depleting substances that contain hydrogen. The nitrous oxide data from CGBAPS and other global sites have been used to quantify the natural/anthropogenic ratio of the sources of oxides of nitrogen (the major sink for ozone) in the stratosphere. The Cape Grim Air Archive has been studied at CGBAPS, at the Commonwealth Scientific and Industrial Research Organisation Division of Atmospheric Research (CSIRO-DAR) and at a number of overseas laboratories (Universities of East Anglia, Heildelberg and California) to verify the real time Cape Grim measurements of ozone depleting substances, to identify a suite of new ozone depleting and replacement species at Cape, and to look at the longest time series of sulfur hexafluoride measurements anywhere in the world, which, because of its extreme atmospheric longevity, can be used to date stratospheric air. Global measurements of ozone depleting substances are carried out in CSIRO-DAR GASLAB facility. The global nitrous oxide data have been used to provide details about global distributions and seasonal trends to date, unobtainable in real time measurements. Gas chromatograph measurements at CSIRO-DAR have found background levels of several major (methyl bromide) and minor ozone depleting species (trace CFCs).

The CSIRO Division of Applied Physics (CSIRO-DAP) has a focus on experimental and theoretical chemical kinetics relevant to atmospheric chemistry. An important area of research is the use of assessment models to examine existing ozone trends and to predict trends by taking into account expected release rates of various trace atmospheric species. Such calculations may require model calculations over decades and a realistic approach is through the use of 2-D models. An important tool developed at CSIRO-DAP is a two-dimensional (2-D) chemical transport model.

CSIRO-DAP has focussed on the way in which the photochemistry is handled in the model and to see how some of the traditional approximations affect the accuracy of the calculations. As a result of this approach, state-of-the-art packages have been developed to determine photodissociation rates and to allow accurately for the way in which chemical reactions vary in importance over a twenty-four hour cycle. The CSIRO-DAP 2-D model is being used to assess a number of scenarios including, calculation of decadal trends in ozone from 1980 to the present and the impact of increasing chlorine and bromine. Results of the calculations show the importance of heterogeneous reactions on sulfuric aerosol particles in determining the calculated ozone trends. In particular, the increase in aerosol levels following the eruption of Mt Pinatubo was shown to have a substantial effect on ozone as a result of the increase in rates of the heterogeneous chemical reactions. The CSIRO-DAP group participated in the NASA Assessment of Atmospheric Effects of Stratospheric Aircraft (AAESA) Programme. The Cooperative Research Centre for the Antarctic and Southern Ocean Environment uses a combination of advanced atmospheric modelling and additional observations to better represent the Antarctic atmosphere and its exchanges with the ice and ocean. Additional data and improved analyses, which are achieved for climate studies, allow improved validation of climate model performance and analysis of the Antarctic stratosphere which, in the region of extensive ozone depletion, has revealed a significant cooling in spring, an increase in vortex winds and a longer lifetime for the vortex.

BIBLIOGRAPHY

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Le Marshall, J. 1989. Satellite Ozone Measurement Techniques. Transactions of the Menzies Foundation, 15, 57-66.

Le Marshall, J.F., Davidson, R.F., Willmott, M.C. and Powers, P.E. 1988. A physically based operational atmospheric sounding system for the Australian region. The Technical Proceedings of the Fourth International TOVS Study Conference Igis, Austria March 16-22. A report from the CIMSS, University of Wisconsin Madison.

Lehmann, P.1994. A Statistical Seasonal Analysis of Winter Decreases in Ozone at Macquarie Island. Geophys. Res. Lett., 21, 5, 381-384.

Lehmann, P., Karoly D.J, Newman P.A, Clarkson T.S. and Matthews, W.A. 1992. Long-term Winter Total Ozone Changes Over Macquarie Island. Geophys. Res. Lett., 19, 14, 1459-1462.

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Sanhueza, E., Fraser, P. and Zander, R. 1994. Source Gases: Trends and Budgets. Scientific Assessment of Ozone Depletion: 1994. WMO Report No. 37 (Chapter 2).

Waugh, D.W. , Plumb, R.A., Atkinson, R.J ., Schoeberl, M .R. , Lait, L. R. , Newman, P.A. , Loewenstein, M., Toohey, D.W., Avallone, L.M., Webster, C.R. and May, R.D.. 1994. Transport out of the lower stratospheric arctic vortex by Rossby wave breaking. J. Geophys. Res., 99 D1, 1071-1088.

Wu, Z. and Le Marshall, J. 1992. Total Ozone from NOAA Satellites in the Australian Region. Aust. Met. Mag., 40, 205-210.