SEASONAL CYCLE OF THE RESIDUAL MEAN MERIDIONAL CIRCULATION IN THE STRATOSPHERE

The transformed Eulerian-mean (TEM) residual circulation is used to st udy the zonally averaged transport of mass in the stratosphere. The re sidual circulation is estimated from heating rates computed with a rad iative transfer model using data from the Upper Atmosphere Research Sa tellite (UARS) as inputs. An annual cycle exists in the resulting circ ulation in the lower stratosphere, with a larger net upward mass flux across a pressure surface in the tropics during northern hemisphere wi nter than during northern hemisphere summer. The annual cycle in upwar d tropical mass flux follows the annual cycle in downward mass flux ac ross a pressure surface in the northern hemisphere extratropics. It is argued that the annual cycle in zonal momentum forcing in the norther n hemisphere stratosphere is controlling mass flux across a pressure s urface in the lower stratosphere both in the tropics and in the northe rn hemisphere extratropics.