We make high-resolution simulations of poorly understood decays of nonlinear atmospheric acoustic–gravity waves (AGWs) after deactivations of the wave forcing. The standard deviations of AGW perturbations, after fast dispersions of traveling modes, experience slower exponential decreases. AGW decay times are estimated for the first time and are 20–100 h in the stratosphere and mesosphere. This requires slow, quasi-standing and secondary modes in parameterizations of AGW impacts to be considered.

The MLT DW1 amplitude is suppressed during El Niño winters in both satellite observation and SD-WACCM simulations. The suppressed Hough mode (1, 1) in the tropopause region propagates vertically to the MLT region, leading to decreased DW1 amplitude. The latitudinal zonal wind shear anomalies during El Niño winters would narrow the waveguide and prevent the vertical propagation of DW1. The gravity wave drag excited by ENSO-induced anomalous convection could also modulate the MLT DW1 amplitude.

In order to have confidence in atmospheric predictions, it is important to know how well different numerical model simulations of the Earth’s atmosphere agree with one another. This work compares four different data assimilation models that extend to or beyond the mesosphere. Results shown here demonstrate that while the models are in close agreement below ~50 km, large differences arise at higher altitudes in the mesosphere and lower thermosphere that will need to be reconciled in the future.

Metal layers occur in the MLT region (80–120 km) from the ablation of cosmic dust. The latest lidar observations show these metals can reach a height approaching 200 km, which is challenging to explain. We have developed the first global simulation incorporating the full life cycle of metal atoms and ions. The model results compare well with lidar and satellite observations of the seasonal and diurnal variation of the metals and demonstrate the importance of ion mass and ion-neutral coupling.

The winter winds over Antarctica form a stable vortex. However, in 2019 the vortex was disrupted and the temperature in the polar stratosphere rose by 50°C. This event, called a sudden stratospheric warming, is a rare event in the Southern Hemisphere, with the only known major event having taken place in 2002. The 2019 event helps us unravel its causes, which are largely unknown. We have discovered a unique behaviour of the equatorial winds in 2002 and 2019 that may signal an impending SH SSW.