Extreme vertical drafts in the polar summer mesosphere: A mesospheric
super bore?
Abstract
The polar summer mesosphere is the Earth’s coldest region, allowing the
formation of mesospheric ice clouds. These clouds produce strong polar
mesospheric summer echoes (PMSE) that are used as tracers of mesospheric
dynamics. Here we report the first observations of extreme vertical
drafts (±50~m/s) in the mesosphere obtained from PMSE,
characterized by velocities more than five standard deviations larger
than the observed vertical wind variability. Using aperture synthesis
radar imaging, the observed PMSE morphology resembles mesospheric bores,
i.e., narrow along propagation (3–4~km) and elongated
(>10~km) transverse to propagation
direction. Additionally, our event presents a large vertical extent (±
3–4~km), resembling a “super bore”. Powerful vertical
drafts, intermittent in space and time, emerge also in direct numerical
simulations of stratified flows, predicting non-Gaussian statistics of
vertical velocities. This evidence suggests that our event, and perhaps
previous bores, might result from the interplay of gravity waves and
turbulent motions.