The Influence of Obliquely Propagating Monsoon Gravity Waves in the Southern Polar Summer Mesosphere After Stratospheric Sudden Warmings in the Winter Stratosphere

Oblique propagation of gravity waves (GWs) refers to the latitudinal propagation (or vertical propagation away from their source) from the low-latitude troposphere to the polar mesosphere. This propagation is not included in current gravity wave parameterization schemes, but may be an important component of the global dynamical structure. Previous studies have revealed a high correlation between observations of GW pseudomomentum flux (GWMF) from monsoon convection and Polar Mesospheric Clouds (PMCs) in the northern hemisphere. In this work, we report on data and model analysis of the effects of stratospheric sudden warmings (SSWs) in the northern hemisphere, on the oblique propagation of GWs from the southern hemisphere tropics, which in turn influence PMCs in the southern summer mesosphere. In response to SSWs, the propagation of GWs at the midlatitude winter hemisphere is enhanced. This enhancement appears to be slanted toward the equator with increasing altitude and follows the stratospheric eastward jet. The oblique propagation of GWs from the southern monsoon regions tends to start at higher altitudes with a sharper poleward slanted structure toward the summer mesosphere. The correlation between PMCs in the summer southern hemisphere and the zonal GWMF from 50 degrees N to 50 degrees S exhibits a pattern of high-correlation coefficients that connects the winter stratosphere with the summer mesosphere, indicating the influence of Interhemispheric Coupling mechanism. Temperature and wind anomalies suggest that the dynamics in the winter hemisphere can influence the equatorial region, which in turn, can influence the oblique propagation of monsoon GWs.

Automated summary

Oblique propagation of gravity waves refers to the latitudinal or vertical propagation from low-latitude troposphere to polar mesosphere. This propagation, not included in current parameterization schemes, may be an important component of global dynamical structure. Studies show a high correlation between GW pseudomomentum flux from monsoon convection and Polar Mesospheric Clouds in the northern hemisphere, indicating the influence of Interhemispheric Coupling mechanism.