An observation-based climatology of middle atmospheric meridional circulation.

Measurements of long-lived trace gases (SF₆, CFC-11, CFC-12, HCFC-12, CCl₄, N₂O, CH₄, H₂O, and CO) performed with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have been used to infer the stratospheric and mesospheric meridional circulation. The MIPAS data set covers the time period from July 2002 to April 2012. The method used for this purpose was the direct inversion of the two-dimensional continuity equation. Monthly climatologies of circulation fields are presented along with their variabilities. Stratospheric circulation is found to be highly variable over the year, with a quite robust annual cycle. The new method allows to track the evolution of various circulation patterns over the year in more detail than before. The deep branch of the Brewer-Dobson circulation and the mesospheric overturning pole-to-pole circulation are no separate but intertwined phenomena. The latitude of stratospheric uplift in the middle and upper stratosphere is found to be quite variable and is not always found at tropical latitudes. The usual schematic of stratospheric circulation with the deep and the shallow branch of the Brewer-Dobson circulation and the mesospheric overturning circulation is an idealization which best describes the observed atmosphere around Equinox. Sudden stratospheric warmings cause increased year-to year variability. [ABSTRACT FROM AUTHOR]