The effects of the QBO on the 3D residual circulation and tracer transport in the stratosphere and mesosphere

The effects of the Quasibiennal Oscillation (QBO) on the three-dimensional (3D) residual circulation and tracer transport in the stratosphere and mesosphere are investigated based on different data sets: simulations with the general circulation and chemistry model HAMMONIA, reanalysis data, and daily-mean wind fields derived from Aura/MLS satellite data. For the latter we use the observed temperature profiles and standard balanced equations, and an optimization of the balanced wind fields via an inversion calculation of the tracer transport based on the observed day-to-day variations of O3 and H2O. The 3D residual circulation is a proxy of the time-mean mass circulation and includes both the Eulerian time-mean flow and the eddy time-mean flow, similar to the zonal mean (2D) residual circulation but with time-mean 3D eddy fluxes used in the Transformed Eulerian Mean (TEM) equations instead of 2D eddy fluxes.

For the winter stratosphere and mesosphere, the results show a pronounced planetary wave-1 structure in the 3D residual circulation at mid- and polar latitudes during QBO-East, and a pronounced planetary wave-2 structure during QBO-West. It is demonstrated that the QBO-induced variations in the 3D residual circulation and eddy mixing are largely responsible for the observed QBO signals in the planetary wave patterns of temperature, geopotential height and tracer distributions. A detailed analysis of the 3D wave driving elucidates the processes leading to the QBO-induced local changes in the time-mean mass circulation. We also find that the OBO-induced local changes in the stratospheric mass circulation leads to a corresponding change in the mass distribution of the troposphere, i.e. to a change in the distribution of high and low anomalies in geopotential height at surface pressure level towards negative phase of North-Atlantic Oscillation when the stratosphere changes from QBO-West to QBO-East.