The reason for this behaviour is an extraordinary dynamic activity at stratospheric heights which is known in atmospheric sciences as a stratospheric warming or, sometimes labelled as “stratwarm”. During such episodes the activity of large sacle waves in the atmosphere strengthens within only a few days or weeks. These so-called pronounced “planetary waves” then cause the global stratospheric circulation to strongly weaken or even to reverse from winter to summer conditions. Since ozone has a relatively long lifetime it can be used as a tracer for atmosphericdynamics.