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Abstract:
Sudden stratospheric warmings (SSWs) are rapid down-welling in the stratosphere and mesosphere. Some SSWs also result in the elevated stratopause (ES) phenomenon - a descent and reformation of the stratopause at a higher-than-climatological altitude. SSW and ES can have a strong effect on stratospheric dynamics and chemistry (including ozone deplating compounds) and influence surface weather for months. The triggers of these phenomena are not sufficiently understood, but observations and modelling suggest that both planetary waves (PWs) and gravity waves (GWs) play a role.
A recent study of Okui et al., 2021 (https://doi.org/10.1029/2021JD034681) used the Japanese Atmospheric General circulation model for Upper Atmosphere Research (JAGUAR) to simulate ES formation during an SSW in the winter of 2018/19. Consecutive 4-day free runs of GW-permitting JAGUAR without GW parameterizations were used. The study showed that forcing due to GWs had a significant effect on the ES appearance that could not have been caused by purely vertical propagation of GWs from tropospheric sources, as most GW parametrizations assume.
In this work, we ray-traced GWs in the aforementioned JAGUAR runs to identify their sources and thus better understand the processes that trigger SSW and ES. Individual GWs in the JAGUAR data were identified using 3-D small-volume wave fitting code (S3D) and used to initialize the GROGRAT ray-tracer. We found that ES was strongly influenced by secondary gravity waves originating from the stratosphere and that although oblique GW propagation played a role, few GWs propagating all the way from the surface contributed to ES formation.
