Tropical stratospheric circulation deduced from satellite aerosol data

Influence of the quasi‐biennial oscillation on isentropic transport and mixing in the tropics and subtropics

“…The effects on planetary-wave breaking have been investigated in a modeling study by O'Sullivan and Chen [1996]. There is direct observational evidence for QBO modulation of tracer fields from volcanic aerosol [Trepte and Hitchman, 1992; Trepte et al, 1993; Hitchman erly QBO winds, their results show a narrow band of very weak mixing associated with the westerlies themselves, adjacent to a region in the summer hemisphere subtropics of enhanced mixing. However, since Haynes and Shuckburgh [2000a] only considered 18 months (less than one QBO period), any suggestion of an influence of the QBO on isentropic transport and mixing had to be speculative.…”

Seasonal formation of nitrous oxide laminae in the mid and low latitude stratosphere

“…Examination of the year-round laminae distributions confirms the well-known seasonal dependence of the surf zone subtropical edge [Waugh, 1996;Bowman and Hu, 1997] : the encroachment of the high lamination region in the winter hemisphere into the deep tropics, and the "quiet zone" separating the winter from the summer hemisphere, found on the summer side of the equator. A regime of rapid meridional transport between low and midlatitudes, governed by synoptic-scale eddies, overlaid by a regime of enhanced tropical isolation above 20 km, was also deduced from satellite observations of aerosol [Trepte and Hitchman, 1992], or trace species [Schoeberl et al, 1997], and modelling studies [Rogers et al, 1998]. …”

Changing transport processes in the stratosphere by radiative heating of sulfate aerosols

“…This quasi-horizontal mixing is the main transport branch for the sulfate aerosol in the lower extratropical stratosphere. Sharp gradients of potential vorticity at the edges of the surf zone act as a transport barrier: the polar vortex at high latitudes inhibits transport to the poles in winter months, and the equatorial jets of the QBO contribute to the formation of a reservoir for chemical species in the lower tropical stratosphere (Trepte and Hitchman, 1992). The formed barrier is strongest in heights from about 21 to 28 km (50 to 15 hPa).…”