Insights on Lateral Gravity Wave Propagation in the Extratropical
Stratosphere from 44 Years of ERA5 Data
Abstract
The study presents (a) a 44-year wintertime climatology of resolved
gravity wave (GW) fluxes and associated zonal forcing in the
extratropical stratosphere using ERA5, and (b) their composite evolution
around gradual (final warming) and abrupt (sudden warming) transitions
in the wintertime circulation. The connection between transformed
Eulerian mean (TEM) equations and the linear GW pseudomomentum is
leveraged to provide a glimpse of the importance of GW lateral
propagation toward driving the wintertime stratospheric circulation by
analyzing the relative contribution of the vertical vs. meridional flux
convergence. The relative contribution from lateral propagation is found
to be notable, especially in the Austral winter stratosphere where
lateral (vertical) momentum flux convergence provides a peak
climatological forcing of up to -0.5 (-3.5) m/s/day around 60oS at 40-45
km altitude. Prominent lateral propagation in the wintertime
midlatitudes also contributes to the formation of a belt of GW activity
in both hemispheres.