Séminaire
The annular modes are the dominant form of tropospheric variability in observations and models, associated with a mass exchange between subtropical and subpolar latitudes and with a latitudinal shift of the extratropical jet stream. Most models exhibit too persistent annular variability, which could also have implications for their sensitivity to climate change. Although it is well known that the slower components of the climate system are key for tropospheric memory, the fact that the nonlinear trosposheric dynamics may also by itself produce low frequency variability is not as widely recognized. In this talk we will show that eddy feedbacks produce persistent annular variability in a simple model with steady forcing and no ocean or stratosphere and we will analyze the mechanisms involved. We will also discuss the extent to which these mechanisms may be relevant for annular mode persistence in observations and for biases in models.
Gwendal Rivière