A NEW PERSPECTIVE ON THE DYNAMICAL LINK BETWEEN THE STRATOSPHERE AND TROPOSPHERE

Atmospheric processes of tropospheric origin can perturb the stratosph ere, but direct feedback in the opposite direction is usually assumed to be negligible, despite the troposphere's sensitivity to changes in the release of wave activity into the stratosphere(1-3). Here, however , we present evidence that such a feedback exists and can be significa nt. We find that if the wintertime Arctic polar stratospheric vortex i s distorted, either by waves propagating upward from the troposphere(4 ) or by eastward-travelling stratospheric waves(5,6), then there is a concomitant redistribution of stratospheric potential vorticity which induces perturbations in key meteorological fields in the upper tropos phere. The feedback is large despite the much greater mass of the trop osphere: it can account for up to half of the geopotential height anom aly at the tropopause. Although the relative strength of the feedback is partly due to a cancellation(7) between contributions to these anom alies from lower altitudes, our results imply that stratospheric dynam ics and its feedback on the troposphere are more significant for clima te modelling and data assimilation than was previously assumed.