Convectively Generated Gravity Waves During Solstice and Equinox Conditions

Abstract Previous studies suggest that mesospheric concentric wave patterns are more observable in the equinox months than solstice months, despite concentric and semiconcentric waves being readily observed in summer months in the stratosphere. This study uses a 3‐D nonlinear model to simulate the propagation and dissipation of convectively generated gravity waves under averaged equinox and solstice conditions to investigate the influences of wave breaking upon these concentric patterns. It is found that the relatively weak atmospheric winds and shears during the equinox months means that waves can propagate up to the lower thermosphere before breaking. In contrast, strong zonal winds and shears in the summer solstice months lead to in situ breaking in the mesosphere, which causes disruption to the concentric pattern. While the western propagating portion of the concentric pattern is filtered by the stratospheric winds, the eastern propagating portion rapidly transitions to turbulence in the mesosphere making it less likely to observe concentric patterns in the solstice months. The concentric pattern is more complete in the equinox months because the waves are only weakly filtered by winds and relatively little in situ breaking occurs in the mesosphere. However, in situ breaking does not affect the pattern in the stratosphere, where the morphology is primarily dictated by wind filtering. This also helps explain why concentric and semiconcentric patterns are observed in the summer stratosphere but not regularly in the mesosphere.