Gravity Wave Variability in the Arctic Mesosphere in Relation with the
Stratospheric Polar Vortex
Abstract
We investigated the variability of short-period (<1 hour)
atmospheric gravity waves (AGWs) in the high-latitude
mesosphere-lower-thermosphere/ionosphere (MLTI) region using OH (3,1)
band emission data from the Advanced Mesospheric Temperature Mapper
(AMTM) at the Arctic Lidar Observatory for Middle Atmosphere Research
(ALOMAR) in Norway. These OH intensity maps from January 2014, 2015, and
2016 were analysed to characterise AGW activity at these altitudes. We
derived phase velocity spectra of AGWs by applying the Matsuda-transform
to the OH intensity maps and calculated spectral power across different
phase speed ranges and propagation directions to study the day-to-day
and intraday variability of AGWs. Our results reveal significant
differences in AGW activity between these years, with 2015 exhibiting
lower spectral power and less variability compared to 2014 and 2016. The
vertical propagation efficiency of AGWs was estimated using principles
of critical-level filtering, incorporating winds from the ERA5 dataset
for altitudes between 0–50 km. The relatively lower AGW activity and
spectral power observed in the MLTI region in 2015 were associated with
higher Arctic Oscillation (AO) index values, suggesting gravity wave
filtering by eastward winds in the upper stratosphere. In contrast,
lower AO index values in 2014 and 2016 indicated minimal filtering,
leading to more diverse spectra of AGWs observed in the OH images. These
findings highlight the strong influence of stratospheric wind structures
on AGW variability in the high-latitude MLTI region during winter.