Sensitivity of a middle atmosphere GCM to consistent scale-interaction of parameterized orographic gravity waves Benjamin Wolf, Erich Becker – Leibniz-Institut of Atmospheric Physics e.V. at Rostock University, email: wolf@iap-kborn.de Summary We find that the circulation in the middle atmosphere is significantly sensitive to the details of the OGW scheme. In particular, the vertical diffusion induced by saturation of OGWs has a considerable impact on the polar night jet during northern hemispheric winter, both by the diffusivity itself and by the secondary effect due to an upward shift of the breaking levels of NGWs. In turn, these changes affect the summer mesopause region by the interhemispheric coupling mechanism. A strong sensitivity of the mesosphere to GWs has also been found in the simulations of sudden stratospheric warmings (McLandress et al. [2012]). The damping of OGWs by boundary layer turbulence and the energy deposition by OGWs are found to be of minor importance. Model Description Difference to conventional parametrizations Classical OGW scheme and extensions  Excitation with subgrid scale orographic perturbation field and resolved near-surface wind  + Wave equations allow long vertical wavelengths  Lindzen saturation hypothesis (Lindzen [1981]): convective instability leads to turbulent vertical heat and momentum diffusion of OGWs  + Wave propagation according to WKB-Approximation: total turbulent vertical diffusion affects OGWs  Momentum deposition, drag, by OGWs (OGWD) affects the resolved flow  + Turbulent diffusion due to saturation of OGWs affects all other scales (resolved large-scale flow, NGWs)  + Energy deposition by OGWs Zonal-mean model climatology from December to February (DJF). (a) Temperature (K, colors) and residual mass streamfunction (contours for -100, -10, -1, +0.001, +0.01, +0.1, +1, +10 +100 Mt s-1) . (b) Zonal wind (m s-1, colors) and complete Eliassen-Palm-Flux (EPF) divergence, including resolved waves and parameterized GWs (contours for -60, -40, -20, -10, -5, 5, 10, 20, 40, 60, 80 m s-1d-1) References M.J. Alexander et al., A Review of Recent Developments on Gravity Wave Effects in Climate Models and the Global Distribution of Gravity Wave Momentum Flux, Quarterly Journal of the Royal Meteorological Society, 2009 E. Becker and U. Burkhardt, Nonlinear Horizontal Diffusion for GCMs, Monthly Weather Review, 2007 E. Becker and C. McLandress, Consistent scale interaction of gravity waves in the Doppler-spread parameterization, Journal of the Atmospheric Sciences, 2009. R. Knöpfel and E. Becker, An idealized radiative transfer scheme for use in a mechanistic general circulation model from the surface up to the menopause region, Journal of Quantitative Spectroscopy Radiativ Transfer, 2011 H. Körnich and E. Becker, A simple model for the interhemispheric coupling of the middle atmosphere circulation, Advances in Space Research, 2010 R.S. Lindzen, Turbulence and Stress Owing to Gravity Wave and Tidal Breakdown; Journal of Geophysical Research, 1981 N.A. McFarlane, The Effect of Orographically Excited Gravity Wave Drag on the General Circulation of the Lower Stratosphere and Troposphere, Journal of the Atmospheric Sciences, 1987 C. McLandress et al., Dynamical control of the mesosphere by orographic and non-orographic gravity wave drag during extended northern winters of 2006 and 2009, Journal of the Atmospheric Sciences, 2012 General influence of parameterized orographic gravity waves Zonal-mean model climatology from December to February (DJF). (a) differences in the orographic wave drag, OGWD (m s-1d-1, colors) between the new and the conventional parametrisation and OGW- induced vertical diffusion coefficient in the control run (contours for 1, 4, 8, 15, 30 m-2s-1d-1) for DJF. (b) Differences in the complete Eliassen-Palm-Flux (EPF) divergence (m s-1d-1, colors) and complete EPF divergence in the control run (contours for - 60, -40, -20, -10, -5, 5, 10, 20, 40, 60, 80 m s-1d-1). OGW