Internal gravity waves influence a variety of phenomena in Earth's stratosphere and upper troposphere, including aviation weather turbulence and the circulations that set high-altitude distributions of ozone and greenhouse gases. Here coupling between the dominant mode of subseasonal variability of the equatorial atmosphere — the Madden-Julian oscillation (MJO) — and subtropical stratospheric gravity waves created by flow over topography is documented for the first time. We use two different meteorological datasets to show that, during Northern Hemisphere winter, the MJO modifies the breaking of internal gravity waves induced by the Tibetan Plateau and the deposition of momentum by these waves into the stratosphere. In particular, the convectively active phase of the MJO in the Indian Ocean is accompanied by gyres that produce stronger eastward winds in the upper troposphere over South Asia; this anomalous eastward flow prevents the nonlinear saturation of gravity waves, allowing them to propagate to higher altitudes. This interaction directly modifies the vertical distribution of gravity wave breaking and momentum deposition but has no significant effect on the vertically integrated wave drag. These results raise new questions about how future changes in tropical rainfall might affect stratospheric variability and highlight the importance of local processes over Tibet for the circulations that set distributions of climatically important high-altitude trace gases.

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*email: naftali.cohen@yale.edu
*Preference: Oral