A chorus of the winds: synchronized oscillations in the Earth’s stratosphere
| Quand ? |
Le 16/11/2015, de 11:00 à 12:00 |
|---|---|
| Où ? | Amphi. Schrödinger |
| Participants |
Peter Read |
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Synchronization occurs when two nonlinear oscillators are coupled and can influence each other's frequency of oscillation. As a result, the oscillators may end up oscillating with a constant phase relationship, or at frequencies maintained in rational ratios. One of the most remarkable examples of such a phenomenon on a planetary scale is found in the Earth's stratosphere. Meteorologists have known since the mid 1960s that the east-west winds in the tropical stratosphere (at altitudes from 10-50 km) reverse cyclically from eastward to westward with an average period of just over 28 months; the result of nonlinear interactions with waves propagating up from the lower atmosphere and known as the Quasi-Biennial Oscillation (QBO). Recent observational studies, however, show that this oscillation is partly controlled by interactions with the seasonal cycle, leading to a form of synchronized behavior so that the period is almost always quantized to half-integer multiples of 1 year, though flips chaotically between different ratios. The physical mechanisms underlying this phenomenon are not well understood in detail, but in this talk I will introduce some of the main ideas and discuss some results from a simplified theoretical model that suggests some likely future trends in the QBO as a result of global warming.