Inter-hemispheric couplings in the middle atmosphere exhibited by principal component analysis of the SD-WACCM-X simulations

This study employs Principal Component Analysis (PCA) and 13 years of SD-WACCM-X model data (2007-2019) to investigate the characteristics and mechanisms of Inter-hemispheric Coupling (IHC) triggered by sudden stratospheric warming (SSW) events. IHC in both hemispheres leads to a cold anomaly in the equatorial stratosphere, a warm anomaly in the equatorial mesosphere, and increased temperatures in the mesosphere and lower thermosphere (MLT) region of the summer hemisphere. However, the IHC features during boreal winter period is significantly weaker than that during austral winter period, primarily due to weaker stationary planetary wave activity in the Southern Hemisphere (SH). During austral winter period, IHC results in a warm anomaly in the polar mesosphere of the SH, which does not occur in the NH during boreal winter period. This study also examines the possible influence of quasi-two-day waves (QTDWs) on IHC. We found that the largest temperature anomaly in the summer polar MLT region is associated with a large wind instability area and a well-developed critical layer structure of QTDW in January. In contrast, during July, despite favorable conditions for QTDW propagation in the Northern Hemisphere, weaker IHC response is observed, suggesting that IHC features and the relationship with QTDW during July would be more complex than that during January.