The impact of the tropical stratosphere on the evolution of the polar night jet

Compared to the lower atmosphere, the stratosphere not only exhibits a substantially different climate but also shows distinctly different variability. This is often seen in the expression of both large and small-scale dynamical processes and by the response to various external forcings. An example of the latter includes increasing stratospheric temperatures due to the rise in greenhouse gas concentrations. Recently, observational support for this has been gained from satellite data, where significant cooling trends have been detected in the upper stratosphere. Processes relevant to the recovery of the ozone layer are also linked to long-term changes in stratospheric temperature. In order to confidently diagnose trends in stratospheric temperature, one must better understand the nature of the stratospheric variability and understand both external and internal drivers of it.

An investigation of the variability of the 60-level stratosphere resolving MetOffice Unified Model has been undertaken. Initial condition ensembles of multi-annual simulations forced by contemporaneous concentrations of greenhouse gases and sea-surface temperature were compiled. We report a link between the phase of the tropical Quasi-Biennial Oscillation and the frequency and nature of sudden stratospheric warmings events.