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The impact of mountains on stratospheric circulation is explored using the Whole Atmosphere Community Climate Model. The Mongolian mountains decrease the boreal winter stratospheric jet strength by approximate to 1/3 and increase the frequency of major sudden stratospheric warmings from 0.08year(-1) to the observed 0.60year(-1). These changes are twice the magnitude of the impacts of the Tibetan plateau and Himalayas. Consistent with the decrease in the zonal jet, there is enhanced Eliassen-Palm flux convergence; this is predominantly from changes in wave propagation pathways through changes to the upper troposphere circulation, not from an increased amplitude of planetary waves reaching the stratosphere. The Mongolian mountains have the greater impact on upper tropospheric circulation due to their meridional location. The Rocky Mountains have no significant impact on the stratospheric jet. Changes in wave propagation in response to the Mongolian mountains are similar to those associated with major sudden stratospheric warming events in observations.

Plain Language Summary The stratosphere is a layer of the atmosphere far from the Earth's surface (10-50km above the surface), but changes in stratospheric circulation, particularly events known as sudden stratospheric warmings, affect the weather and climate at the surface. By flattening individual mountain regions in a climate model that extends from the Earth's surface far past the stratosphere, we study the effects of mountains on stratospheric circulation and the frequency of sudden stratospheric warming events. We find that the presence of the Mongolian mountains weakens the stratospheric jet by a third of its strength and creates 6 times more warming events as there would be without these mountains. The impact of the Mongolian mountains is about twice as large as the impact of the larger and more expansive Tibetan plateau and Himalaya. Mountains are a source of planetary-scale atmospheric waves that propagate upward into the stratosphere; we find that the mountain effect on the stratosphere is largely because the mountains alter the pathway that all waves take as they propagate toward the stratosphere, through the influence the mountains have on circulation lower down in the atmosphere. We find similar anomalous wave propagation during sudden warming events in the model and observations.