Group Leader: Marco Giorgetta

Waves play an important role in the atmospheric dynamics. They can propagate from source regions over considerable horizontal or vertical distances until they are dissipated by damping mechanisms. Where the damping happens, the heat and momentum fluxes carried by the waves modifies the circulation. Examples of wave driven circulations are mid-latitude jets and the quasi-biennial oscillation (QBO) in the tropical stratosphere, and the polar night jets are strongly influenced by gravity waves emitted from the troposphere below. Our group is interested in such wave effects on the atmospheric circulation, with the current research focused on the QBO.

The QBO consists of downward propagating westerly and easterly jets which result form the interaction with an upward propagating wave spectrum, for which deep convection in the tropics is the primary source. The QBO can also modulate the wind shear and stability of the tropical tropopause layer with effects on the deep convection. We are interested in both problems, the details of the wave meanflow interaction producing the QBO, and the mechanism by which the QBO affects deep convection.

The research in our group is linked to the work of the Cloud and Convection group, due to the role of convection as the main wave source, and to the Global Circulation and Climate group working on the thermodynamic drivers of the global circulation, in which the QBO – convection system is embedded.

The research is organized along two lines, which both will make use of high resolution simulations permitting the explicit simulation of deep convection:

1. Exploring the details of the wave meanflow interaction that generates the QBO in “direct” QBO simulations. Here “direct” refers to the direct modelling of the entire wave spectrum that is expected to contribute to the QBO. The focus will be on the analysis of the contribution of different wave types and scales to the life cycle of the QBO.
2. Research on the mechanism leading to the observed effects of the QBO on tropical convection and indirectly to signals in the tropospheric circulation in the wider region. Here experiments with externally controlled QBO states will be used to study the response of tropical conditions to the modified conditions in the tropical tropopause layer.