The large-scale circulation of the middle atmosphere is characterized by fast zonal winds and a much slower meridional circulation, with upward motion across the tropical tropopause and a poleward and downward motion in the stratosphere.

Climate models predict an acceleration of the middle atmosphere circulation over recent and coming decades due to changes in greenhouse gases and ozone-depleting substances, but existing observations do not provide a clear picture. Better understanding of the processes driving the stratospheric circulation and variability now and in the changing climate is therefore of high importance.