Chapter 5 Climate Research

WCRP Activities > Stratospheric Processes and their Role in Climate (SPARC)

The Stratospheric Processes and their Role in Climate (SPARC) program of WCRP involves studies of the interaction of dynamical, radiative and chemical processes in the stratosphere and upper troposphere, as well as their impacts at the surface. The SPARC program includes work on the depletion of stratospheric ozone which is very relevant to Australia. The Bureau of Meteorology maintains the national ozone observation program that provides basic data for SPARC studies. The program involves surface and satellite measurements of total ozone across Australia, and ozonesonde observations are taken regularly at Melbourne. The Bureau and the Australian Antarctic Division (AAD) collaborate to maintain an ozonesonde program at Macquarie Island.

Using the routine data on stratospheric ozone in association with the output from the operational global numerical weather prediction model, a system to analyse and predict UV levels at the surface continues to be developed in BMRC (Figure 5.12). Research in the University of Tasmania and AAD aims to parameterise the effect of UVB radiation on microbial communities in the coastal waters of Antarctica. Data from a field study in 2002-03 are being analysed and compared with a model of carbon productivity.

Figure 5.12. A typical daily pattern of clear sky UV Index from the Bureau of Meteorology.

Gravity waves play an important role in the dynamics of the stratosphere, and researchers at Adelaide University are directly involved in a SPARC project aimed at improving our understanding of gravity waves in the atmosphere. Ground-based radar and high-resolution radiosonde data are used to estimate the sources and fluxes of gravity waves in the troposphere and lower stratosphere, and a global climatology of wave activity in the lower stratosphere has been produced. Convection is a source of gravity waves, and the Darwin Area Wave Experiment (DAWEX) was a SPARC field experiment aimed at quantifying the generation of gravity waves by deep tropical convection. During DAWEX in late 2002, in Darwin, researchers from Adelaide University, BMRC, USA and Japan used a variety of ground-based, in situ and modelling techniques to study convectively generated waves and their propagation into the middle and upper atmosphere.

There has been research in BMRC to improve the representation of the stratosphere in models. The work has included collaboration with other organisations aimed at identifying the sources of uncertainty in modelling stratospheric processes. The GCM Reality Intercomparison Project for SPARC (GRIPS) is being completed in 2003, and it is found that the structure of the polar vortex in models varies with the representation of gravity-wave drag, the top level and the vertical resolution in the model. BMRC is hosting a project under the auspices of WGNE that complements GRIPS by focusing on predictability in the stratosphere. It is found that the representation of the stratosphere affects overall quality of model prediction, and the accuracy of prediction is improved by higher vertical resolution and a higher top level for the model.

The University of Wollongong operates a complementary site of the international Network for the Detection of Stratospheric Change (NDSC) aimed at monitoring longterm variability and change in the composition of the stratosphere using ground-based remote-sensing instruments. The site at Wollongong involves solar, infrared, visible and UV spectroscopy.

Analysing data from the Cape Grim Baseline Air Pollution Station (BAPS), CAR scientists have found that concentrations of chlorofluorocarbons (CFCs) in the atmosphere have begun to decline for the first time (Figure 5.13). Chlorinated organic trace gases are the major chemical drivers of stratospheric ozone depletion, and analysis of background air at Cape Grim combined with firn air from Antarctica shows that tropospheric organochlorine levels peaked in the mid-1990s and are now declining steadily. It is expected to take another fifty years for organochlorine levels to fall to the levels of the early 1980s, when anthropogenic sources of these species were first introduced.

Figure 5.13. Cape Grim record of CFC-11 in clean (background) air. The reduction in concentration of this significant ozone depleting substance since the early 1990s resulted from the international protocols established in the 1980s. (Courtesy CSIRO Atmospheric Research).