Summary
Missing gravity wave drag near 60 degrees south has been proposed as the cause of the common cold bias in modelled southern polar stratospheric temperatures [McLandress et al. 2012]. Potential gravity wave momentum sources around those latitudes, such as jets, fronts and orographic waves generated by small islands, have become a focus of gravity-wave source investigations. Macquarie Island provides opportunities for such gravity wave studies through both the waves it generates as a knife- edge like barrier in a strong oceanic wind flow, and as a site where regular balloon soundings provide observational insight into waves propagating overhead [e.g. Guest et al, 2000]. High resolution (horizontal grid spacing of 1 km) ACCESS model runs, nested within the coarse global ACCESS grid, make it possible to investigate the nature of gravity waves generated in the vicinity of Macquarie Island. Momentum flux measurements are used to identify strong wave events and the character of the waves generated by the candidate mechanisms above is examined. An alternate method for extracting the momentum flux using temporal rather than spatial averaging is also being trialled. This presentation will describe the methods used for this study and preliminary results. References: Guest, F. M.; Reeder, M. J.; Marks, C. J. & Karoly, D. J. Inertia-gravity waves observed in the lower stratosphere over Macquarie Island Journal of the Atmospheric Sciences, 2000, 57, 737-752. McLandress, C.; Shepherd, T. G.; Polavarapu, S. & Beagley, S. Is missing orographic gravity wave drag near 60deg S the cause of the stratospheric zonal wind biases in chemistry-climate models Journal of the Atmospheric Sciences, 2012, 69, 802-818.
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