Global Responses of Gravity Waves and Zonal Mean Winds to the Madden-Julian Oscillation and the Latitudinal Dependence of Their Relations Using MERRA-2

Using 17 years of Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data, significant responses of gravity wave (GW) variances, zonal winds and parameterized GW drag to the Madden-Julian Oscillation (MJO) are identified globally during boreal winter, and their relations are examined. The relative anomalies of GW variances range from -4% (phase 7) to 8% (phase 4) in tropics, and -20% (phase 1) to 20% (phase 5) in the northern polar region (NPR). The anomalies of zonal winds are from -3-3 m/s and -4-8 m/s in tropics and NPR, respectively. The vertical and latitudinal structures of MJO signals in GW, wind and GW drag show coherent patterns. Further analysis implies that in the NPR, the eastward wind leads to westward momentum flux carried by the GWs. This flux leads to westward drag, which drives that of zonal winds and imprint the MJO signal in GWs to the wind. Plain Language Summary Atmospheric gravity waves (GWs) are oscillations of the atmosphere that are generated by the disturbances such as wind flowing over mountains, thunderstorms, etc., and propagate upward. They play an important role in the dynamics and coupling of the atmosphere. The Madden-Julian-Oscillation (MJO) is a tropospheric intraseasonal oscillation that is characterized by eastward propagating deep convections and coupled circulations. Tropospheric convections and wind circulations associated with MJO has been known to modulate the sources and propagation of GWs. MJO is a tropical phenomenon, yet the modulation of GWs extend to the high latitude region. Using 17 years of reanalysis of modern satellite observations of the atmosphere data of temperature and winds, significant MJO signals are found in GWs, zonal winds and the driving of GWs to the wind globally during boreal winter, and their relations are examined for the first time. It is found that in the northern hemisphere polar region, the winds are eastward. These winds cause the GWs to carry westward momentum. These momentum drives the wind westward and project the MJO signals in GWs to the zonal winds. This mechanism causes the MJO signal in GWs and the driving of GW to the wind to have opposite signs. Key Points Significant responses of gravity wave (GW), zonal wind and parameterized GW drag to Madden-Julian Oscillation (MJO) are found globally, structured with latitude and altitude MJO induces similar to 12% change of GW variance in tropics (P4-P7), and 40% (P5-P1) in PR at similar to 50 km, which are 6 (P4-P7) and 12 m/s (P2-P7) for wind The eastward winds in the NH polar region cause GW to have westward momentum, induces westward drag, which imprints the MJO signal to winds

Automated summary

Using 17 years of Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data, significant responses of gravity wave (GW) variances, zonal winds and parameterized GW drag to the Madden-Julian Oscillation (MJO) are identified globally. The relationships between these variables are studied, showing coherent patterns. In the northern polar region, eastward winds lead to westward momentum flux carried by GWs, resulting in westward drag and imprinting MJO signals in zonal winds.