1Institute of Environmental Physics University of Bremen, Bremen, Germany
2National Institute of Water and Atmospheric Research Ltd, Lauder New Zealand
3Institute of Meteorology and Climate Research, Forschungszentrum Karlsruhe and University of Karlsruhe, Karlsruhe, Germany
4Department of Chemistry University of Wollongong, Wollongong, Australia
5Global Environment Division National Institute of Information and Communications Technology (NICT), Tokyo, Japan
6Department of Physics and Astronomy, University of Denver, Denver, Colorado, USA
7Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Abstract. We present long-term time-series of strato-mesospheric CO vertical columns measured from stations located in Antarctica, mid-latitudes and the Arctic, covering the period from 1997–2005. The instrument and the measurement technique allows the separation of tropospheric and strato-mesospheric contributions to the CO column, therefore providing information on the chemistry and dynamics both at low and high altitudes. Data from polar stations show a similar annual variability of strato-mesospheric CO with a strong maximum in late winter and spring and a small enhancement in late summer for some stations, which we call the "summer bulge''. Generally, the mid-latitude stations show no significant annual variability of strato-mesospheric CO columns. Measurements were compared with a two-dimensional chemistry-transport model of the middle atmosphere. The annual and latitudinal variations of CO are reproduced very well by a model run including thermospheric CO. Comparison with different model scenarios show that the polar winter maximum is due solely to downward transport of thermospheric CO, while the summer maximum is due to CHOx chemistry in the stratosphere.