Stratospheric circulation is investigated by further analyses of three years of Stratospheric And Mesospheric Sounder (SAMS) data.
1. In the upper stratosphere and lower mesosphere during NH summer/autumn, clear pulses of enhanced mixing ratio (related to an apparent coupling of semiannual oscillation (SAO) and annual oscillation (AO) components) appear to propagate from the low northern latitudes into both hemispheres. The behavior is similar to that predicted by diabatic models under equinox conditions.
2. The lack of a clear SH spring "double peak" in methane (CH4) and nitrous oxide (N2O), compared with that observed in the NH spring, is attributed to enhanced tropical concentration in October caused by vertical transport from the SAO, combined with a stronger NH summer/autumn AO component.
3. Evidence is found for significant NH autumnal vertical and poleward transport at high latitudes in the lower mesosphere.
4. Eddy effects on constituent transport are investigated with two transport formulations:
(a) The Transformed Eulerian Mean formulation, together with calculated residual mean winds, is used to delineate regions/times of significant eddy contributions to constituent transport. Significant regions are found in the stratosphere in all seasons, not only in the NH winter high latitudes (where contributions from non-linear and non-steady perturbations in sudden and final warming events are expected), but also in the midlatitude, middle stratosphere in autumn and at winter-summer low latitudes near the stratopause. Large magnitudes near the stratopause during solstice suggest that the use of diabatic or residual winds may be inadequate for describing mass transport at these heights.
(b) The effective transport formulation is used to calculate the effective transport velocity and the "eddy diffusion coefficient for CH4 and N2O. The highly variable nature, in time and space, of the derived fields underscores questions about the use of the eddy diffusion concept in large scale models for understanding middle atmosphere constituent circulation. The results from this study show, however, that carefully determined fields for may lead to a better approximation to the middle atmospheric circulation than is provided by diabatic or residual mean formalisms.