Recent studies suggest the importance of horizontal propagation of gravity waves (GWs), especially in high latitudes of the winter Southern Hemisphere (SH), although most standard gravity wave parameterizations (GWPs) treat GW simply as vertical. In this study, a new orographic GWP including three-dimensional GW propagation is developed and its impact on large-scale dynamical fields is examined. Our GWP calculates the horizontal location and change of wavenumbers of GWs explicitly by vertical integration of the ray tracing equations, and the body forces due to horizontal refraction of GWs, that exist even without dissipation. In addition, the computational cost for ray tracing is greatly reduced by effective parallelization using Taylor’s series approximation for background fields of the ray tracing. Two numerical experiments are performed by Model for Interdisciplinary Research of Climate (MIROC)-AGCM, to which the new orographic GWP and a conventional one are respectively implemented. For the experiment with the new GWP, westward forcing above the core of the polar vortex in the Southern Hemisphere is enhanced in winter. This is mainly because latitudinal propagation of parameterized GWs which amounts to 30 degrees at most toward the axis of the jet. It is also shown that the forcings produced by the refraction contributes to the significant amount. The zonal wind in SH winter is slightly stronger in the polar upper stratosphere for the experiment with the new GWP, which is consistent with the differences in the GW forcings. The strength and seasonal evolution of polar vortex is less affected by the GW forcings possibly because of the compensation by EP flux divergence by resolved waves. These results suggest the potential importance of the three-dimensional propagation in GWPs for better representation of the momentum budget of the middle atmosphere in climate models.

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*email: kaoru@eps.s.u-tokyo.ac.jp
*Preference: Poster