Filling a hole in climate models
Gravity waves are small scale atmospheric waves that play a critical role in transferring momentum throughout the atmosphere. Climate models (which represent our atmosphere in programs that can be run on computers) cannot fully describe the atmosphere without the inclusion of gravity waves. However, these waves are generally of a horizontal scale that is much smaller than the area represented in a model. As a result, they cannot be represented directly and parameterisation schemes, where gravity wave processes are distilled into a few physical quantities, are used to represent their generation, propagation and dissipation.
Gravity waves are very difficult to observe to the extent required by climate models. The complexity of global climate and weather prediction models makes the task of accurately representing the effect of these waves even more difficult. As a result, climate models of the atmosphere use gravity wave parameterisation schemes that only loosely resemble observations and that cannot react to changes in climate that will alter their sources. While this is the case, the realism of modelled responses to climate change cannot be assured.
This project brings together the need for observations that can be used to improve gravity-wave parameterisation and the capacity for instruments at Davis to make observations of relevant gravity wave parameters. Space-based instruments will be used to combine a global perspective with high resolution local observations.
This project seeks to use atmospheric instruments available at Davis station and beyond to provide observational limits for gravity wave parameterisation schemes used in numerical climate and weather prediction models and to thereby improve predictions of atmospheric change.
To achieve this, the project will:
- expand the base of gravity wave observations relevant to gravity wave parameterisation schemes using the suite of instruments at Davis and compare those observations to those made from space;
- use our observations to measure gravity wave source characteristics both directly and by employing ray-tracing techniques to relate middle atmosphere waves to source regions lower in the atmosphere;
- engage with the modelling community about the issues associated with gravity wave parameterisation schemes. This will include both scheme developers and end users; and
- relate these observations to gravity wave parameterisations schemes and suggest improvements to the schemes.
The project will enhance our capabilities in selected areas to achieve these goals:
- A gravity wave ray-tracing capability will be developed using publicly available software and novel techniques for assimilating our data into a model of the atmosphere through which the waves propagate.
- An airglow imager will be installed by one of our international partners to allow high resolution images of gravity waves to be collected from the dark polar mesosphere.
Our atmospheric instruments at Davis station, some new instruments to be deployed there by our international partners, and global satellite observations, will enable us to provide observational limits on the gravity wave parameterisation schemes used in climate (and weather prediction) models. By providing an interface between models and observations, we will help craft the next generation of parameterisation schemes and so improve predictions of atmospheric change.