Instraseasonal Variation in Stratospheric Gravity Waves and Zonal Winds tied to the Madden-Julian Oscillation

The Madden-Julian Oscillation (MJO) dominates tropical intraseasonal precipitation variability, and it is accompanied by characteristic wind anomalies in the troposphere. Previous research has identified two-way coupling between the Madden-Julian Oscillation (MJO) and the stratosphere: Zonal winds in the lower stratosphere have been linked to modulation of MJO precipitation anomaly strength, and eastward migrating regions of enhanced stratospheric gravity wave variance have been observed to follow MJO intraseasonal precipitation and tropopause zonal wind anomalies. Here, the origin of observed intraseasonal gravity wave variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments are designed to test wave filtering and wave generation hypotheses relating tropopause winds to observed stratospheric gravity wave variance. All experiments use identical convective latent heating but vary the large-scale horizontal wind profile to investigate relationships between stratospheric gravity waves and zonal winds at different levels. The results show that gravity wave variance in Atmospheric Infrared Sounder (AIRS) data is primarily sensitive to upper stratospheric zonal wind variations, while tropopause wind variations have only a relatively small effect. Neither the wind filtering mechanism nor the obstacle source effect appears to be responsible for the observed intraseasonal variations in AIRS stratospheric waves. The results suggest a relationship between stratospheric and tropopause winds above MJO precipitation anomalies. Further investigation reveals a previously unidentified intraseasonal variation in stratospheric zonal winds tied to the phase of the MJO. The results have implications for gravity waves in different scale and frequency bands, their relationship to MJO precipitation anomalies, and their effects on atmospheric circulation.