Direct Observation of Quasi-monochromatic Gravity Wave Packets
Associated with the Polar Night Jet using a Doppler-Rayleigh lidar
Abstract
An advanced hodograph technique was applied to extract
quasi-monochromatic, linear gravity wave (GW) packets from simultaneous
wind and temperature measurements by a ground-based
Doppler-Rayleigh-Mie-Raman lidar located in Kühlungsborn
(54\,\textdegree N,
12\,\textdegree E). During the night of 11 to
12 February 2022, the stratospheric polar vortex was slightly elongated
towards Central Europe. The polar night jet’s (PNJ) core was located
nearly above the lidar. This unique meteorological situation allowed
horizontal wind and temperature measurements in a stratospheric
high-wind speed regime. GW refraction in the strong vertical gradient of
the horizontal winds associated with the PNJ was observed. In addition,
the subsequent low-pass filtering of upward and downward propagating GWs
in the strong winds of the PNJ was demonstrated. A pair of upward and
downward propagating GWs at the top and bottom edge of the PNJ’s core
could be the result of shear excitation in the PNJ. A statistical
analysis of intrinsic GW parameters is provided for all resolved linear
GWs. Approximately 35\,\% of the resolved GWs
propagate downward, and there is stronger filtering of the downward
waves compared to the upward waves by the PNJ core. ECMWF-IFS horizontal
winds and temperatures had a lower variability than the lidar and a
poorer overall agreement above 50\,km. Stratospheric
temperatures in ECMWF show a cool bias of greater than
2\,K.