Atmos. Chem. Phys. Discuss., 13, 729-763, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Water vapour and the equatorial mesospheric semi-annual oscillation (MSAO)
R. L. Gattinger1, E. Kyrölä2, C. D. Boone3, W. F. J. Evans4,5, K. A. Walker3,6, I. C. McDade7, P. F. Bernath3,8, and E. J. Llewellyn1
1ISAS, Department of Physics and Engineering Physics, 116 Science Place, University of Saskatchewan, Saskatoon SK, S7N 5E2, Canada
2Finnish Meteorological Institute, Earth Observation, P.O. Box 503, 00101, Helsinki, Finland
3Department of Chemistry, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
4NorthWest Research Associates Inc., 4118 148 Avenue N.E., Redmond WA 98052, USA
5Centre for Research in Earth and Space Science (CRESS), York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada
6Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 1A7, Canada
7Department of Earth and Space Science and Engineering (ESSE), York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada
8Department of Chemistry and Biochemistry, Old Dominion University, 4541 Hampton Boulevard, Norfolk, Virginia 23529-0126, USA

Abstract. Observations of the mesospheric semi-annual oscillation (MSAO) in the equatorial region have been reported dating back several decades. Seasonal variations in both species densities and airglow emissions are well documented. The extensive observations available offer an excellent case study for comparison with model simulations. The broad range of measurements is summarised with emphasis on the 80 to 100 km region. Photochemical model simulations are described for near-equinox and near-solstice conditions, the two times with notable differences in the observed MSAO parameters. Diurnal tides are included in order to facilitate comparisons of observations made at different local times. The roles of water vapour as the "driver" species and ozone as the "response" species are examined to test for consistency between the model results and observations. The model simulations suggest the interactions between eddy mixing and background vertical advection play a significant role in the MSAO phenomenon. At the equator, 90 km altitude, the derived eddy mixing rate is approximately 1 × 106 cm2 s−1 and vertical advection 0.8 cm s−1. For April the corresponding values are 4 × 105 cm2 s−1 and 0.1 cm s−1.

Citation: Gattinger, R. L., Kyrölä, E., Boone, C. D., Evans, W. F. J., Walker, K. A., McDade, I. C., Bernath, P. F., and Llewellyn, E. J.: Water vapour and the equatorial mesospheric semi-annual oscillation (MSAO), Atmos. Chem. Phys. Discuss., 13, 729-763, doi:10.5194/acpd-13-729-2013, 2013.
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