Gravity wave drag parameterization in models of the quasi-biennial oscillation

A major failing of large-scale general circulation models (GCMs) of the atmosphere has been their inability to simulate phenomena such as the quasi-biennial oscillation (QBO). This is an oscillation between westerly and easterly zonal mean winds observed in the equatorial stratosphere. It is driven by vertically-propagating waves (planetary-scale waves and gravity waves) which transport momentum and energy upwards from the troposphere. Gravity waves, because of their small scale, are generally unresolved in GCMs, so for the models to be able to simulate the QBO, the drag due to these waves must be accounted for by means of a parameterization. I have been studying gravity wave drag parameterization schemes and I shall give an overview of my work in this talk. I have determined the constraints that are needed for each of these schemes to be able to generate a QBO in a one- or two-dimensional model. These constraints can be generalized ultimately for improving the representation of gravity wave drag in GCMs. I shall also discuss a model for the QBO that I am developing, which is based on nonlinear interactions of upward-propagating waves at their critical levels.

Please attend this seminar to be given by Dr. Lucy Campbell. She is a candidate for a UFA in the Department of Mathematics.