Investigating ozone depletion above Davis
A new program of stratospheric ozone studies has been established at Davis by the AAD's Space and Atmospheric Science (SAS) group and the Bureau of Meteorology (BoM). This effort represents the first time Australia has made in-situ measurements of stratospheric ozone in Antarctica, and is part of the larger investigation of the composition, dynamics and climate of the middle atmosphere being undertaken at Davis by the SAS program.
The program makes use of balloon-borne ozonesondes launched by BoM staff at Davis to profile ozone concentration from the ground to altitudes of up to 35km. Ozonesondes are a well-established means of measuring ozone, and are regularly launched at about 40 stations world-wide, including 9 in Antarctica. At the heart of each ozonesonde is a chemical cell containing a dilute solution of potassium iodide. Air is passed through the cell by a pump, and a reaction takes place between ozone and the solution which produces an electrical current proportional to the ozone concentration. A standard meteorological radiosonde is incorporated in the balloon payload, and this provides additional data on pressure, temperature and humidity during the flight. The readings, together with signals from an on-board GPS receiver which provide location information for the determination of wind speed and direction, are telemetered to a ground receiving station.
The operational aspects of the Davis program are being coordinated by the Bureau's Ozone Monitoring Unit (OMU). Through the OMU, the Bureau maintains an extensive and long-term commitment to ozone measurement, including programs of ozonesonde launches at Macquarie Island and Melbourne, and ozone total column abundance measurements at Macquarie Island and five Australian centres. Importantly, Macquarie Island is the only subantarctic site from which ozonesondes are launched.
The Davis ozone study has three main aims;
- To investigate the influence of atmospheric gravity waves and planetary waves on ozone depletion, and the climatology of ozone above Davis. Although there is a broad understanding of the processes that lead to ozone depletion, there are still discrepancies between observations and model predictions. This limits the usefulness of models in predicting future ozone levels. Aspects of these discrepancies may relate to small-scale thermodynamic processes associated with the action of natural wave processes in the atmosphere. The ozone measurements at Davis combined with data from the LIDAR and the recently commissioned VHF radar will provide new data on these processes.
- To provide local ozone data to aid in the derivation of temperature profiles from the Davis LIDAR, and to provide in-situ temperature measurements in the upper stratosphere for comparison with LIDAR observations. These measurements will contribute to assessing the long-term climatology of the stratosphere above Davis.
- To contribute to international efforts in the understanding of ozone depletion through participation in the European Union program 'Qualitative Understanding of Ozone Losses by Bipolar Investigations' (QUOBI), and contribution of data to the World Ozone and Ultraviolet Radiation Data Center.
The ozonesondes are currently being flown monthly, and from mid-June to mid-October the flights will be made at weekly intervals to coincide with the time of maximum interest in ozone levels. The launch schedule will be coordinated with operation of the Davis LIDAR and activities of the QUOBI program. QUOBI is an international effort led by Germany's Alfred Wegener Institute for Polar and Marine Research that involves regular ozonesonde launches by Antarctic and Arctic stations during their respective winter and spring seasons. The ozonesondes launched by stations in the QUOBI program attempt to sample the ozone concentration in parcels of air that are carried from one observing site to another by the stratospheric flow, thereby providing information for the refinement of chemical models of the atmosphere.
A further important aspect of the Davis program will involve collaborative research with Chinese scientists who are operating a program of ozone total column abundance measurements using a ground-based spectrophotometer at Zhong Shan station near Davis. Comparison of data from the two sites will enable calibration and consistency checks for the different measurement techniques that are employed.
The first ozonesonde was successfully launched on 20 February 2003, and we look forward to the exciting new data to follow.
Andrew Klekociuk, Space and Atmospheric Science Program, AAD