Atmospheric processes and change
As we learn more about our atmosphere, connections between different layers and latitudes highlight the complex interactions that occur within it. Atmospheric processes that extend over scales bigger than weather systems, and beyond the time scales of forecast cycles, link local weather to regions as remote as Antarctica. If we are to make accurate predictions on the impact of climate change, we need to adequately understand these processes and the atmospheric layers within which they operate.
The variable nature of our atmosphere is part of our daily lives. Some of this variability is understood in terms of regional and hemispheric-scale patterns (such as the El-Nino Southern Oscillation) but the processes that drive these patterns require more investigation. The vertical reach of these patterns includes the Antarctic stratosphere, a region that is (and will be for some time to come) significantly affected by the springtime destruction of ozone.
Numerical models (which use physical observations and mathematical equations to represent a system) of our atmosphere allow us to study the climate's response to changing conditions. These models are being asked to represent increasingly complex processes throughout more of the atmospheric column. New observations are needed to provide a test bed for the expansion of model domains.
This research stream will improve:
- understanding of ‘teleconnections’ (where weather changes at one location are linked to changes elsewhere) between Antarctic and Southern Ocean weather systems, to provide data for use in weather predictions and climate projections for Australia;
- understanding of the connections between ozone concentrations and characteristics of the polar vortex (a region in the stratosphere, 15-50 km up, where strong winds around the pole prevent air mixing with the rest of the atmosphere). This will enable improved projections of the climate system response to ozone recovery, and changes to wind patterns and storm frequencies at high southern latitudes;
- representation of atmospheric processes in numerical models; particularly energy and momentum transfer, chemical transport and links between regions and hemispheres.
The stream is divided into two linked research areas:
- Characterising atmospheric processes, variability and change
- Model development for weather and climate predictions
Each of these research areas will, in part, be directed by the needs of the other.
Characterising atmospheric processes, variability and change
Photo: Gary Miller
This research is focusing on two key questions:
- What are the patterns of variability and change in the high-latitude Southern Hemisphere atmosphere?
- What processes drive change and variability?
To answer these questions we are:
- Studying the drivers of regional and hemispheric climate variability – the El-Nino Southern Oscillation (ENSO), the Southern Annular Mode (SAM) and the Pacific Decadal Oscillation (PDO). These climate patterns are associated with a redistribution of energy in the lower atmosphere and can affect the wave-driven circulations higher in the atmosphere.
- Studying the thermal and dynamical state of the Antarctic atmosphere over many seasonal cycles and several solar activity cycles, to help validate climate model simulations and to separate sources of natural climate variability from human-induced change.
- Investigating the climate response to restored ozone levels. Ozone recovery during the next decade will influence the future climate of the Southern Hemisphere, although the magnitude of this influence is unclear.
Model development for weather and climate predictions
Photo: Simon A.
The research is focusing on two key questions:
- What high latitude processes need to be better characterised to improve atmospheric models for weather and climate prediction?
- What atmospheric observations are required to better validate the next generation of models?
These questions will be investigated by:
- Improving our understanding of Antarctic and Southern Ocean processes such as the evolution of polar low pressure systems, the processes that lead to the formation and variability of frontal systems and the radiative properties of cloud and aerosol particles.
- Observations of the boundary between the Upper Troposphere and the Lower Stratosphere (UTLS) and of the atmosphere above. These will improve our knowledge of the processes that link our weather to the stratosphere. Air exchange can influence the role greenhouse gases play in the region. Ozone destruction affects both the chemical and dynamical state of the stratosphere, both of which are poorly represented in climate models.
- Studying the role of atmospheric waves that are too small to be included in long-term simulations of climate but that are vital in driving atmospheric circulations. Climate models cannot accurately represent the chemistry of the southern springtime polar stratosphere possibly due to the way small-scale waves (known as gravity waves) are represented. Observations of these waves are needed to improve their representation in models.
These investigations will contribute to the next generation of climate models, both through the improved direct representation of physical processes and the definition of processes that fall below the natural spatial scales these models can represent.