Variability and changes of the stratospheric large scale circulation and possible consequences for ozone streamer events

Planetary waves (PW) dominate the meridional Brewer-Dobson circulation in the stratosphere and therewith, the large-scale mass transport of ozone. As PW break, ozone poor air masses are irreversibly mixed into mid-latitudes. Due to the disproportionate warming of the North Pole, an increase in PW activity (PWA) is expected. This should also have consequences for ozone streamer events.

We derived the PWA of ERA 5 and Interim Reanalysis temperature from ground level up the mesosphere. We identify Ozone-streamer events with a statistical based approach on the basis of total column concentration measured by GOME-2. We deconvoluted the time series of the PWA and the ozone-streamer events with the empirical mode decomposition method (EMD). Moreover, we developed a simple spectral model of the meridional wind shear on the basis of PW. This model serves as a measure of the atmospheric instability in the stratosphere.

As we deconvolute the PWA with the EMD we find signatures of QBO, ENSO and solar cycles and quantify their contributions. As PW dominate the circulation in the stratosphere, it appears to be a coherent consequence that ozone streamers are modulated on the same time scales as the PWA.With the spectral model of the meridional wind shear we find regions in the atmosphere, where PW are most likely to break. As a result there is an increased meridional transport of air masses, in particular of ozone. This is why ozone streamers occur most frequently at the transition zones from ocean to continent; strongest from North Atlantic to Europe. Moreover, we find significant long-term trends of the PWA in the stratosphere. Due to the increase of the PWA in the stratosphere, ozone streamer events are likely to occur more often in the future.