​​Gravity Wave Variability in the Arctic Mesosphere in Relation with the Stratospheric Polar Vortex​

In this study, we have investigated short-period ( 1 hr) atmospheric gravity waves (AGWs) in the Arctic mesosphere-lower thermosphere (MLT) region during January of 2014, 2015, and 2016. We used OH (3,1) band emission data from the Advanced Mesospheric Temperature Mapper (AMTM) at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR), Norway. By applying a three-dimensional spectral analysis technique (Matsuda-transform), we derived phase velocity spectra of AGWs and characterized both intraday and day-to-day variability by examining wave power across multiple directional bins and phase speed ranges. Our results reveal significant year-to-year differences in AGW activity with markedly reduced spectral power and shifted propagation directions in January 2015 compared to 2014 and 2016. We compared these wave characteristics with the directional distribution of critical-level filtering between 0 and 50 km, utilizing ERA5 reanalysis winds and with the Arctic Oscillation (AO) index. We found that dominant wave propagation directions closely aligned with critical-level filtering below 50 km and that the reduced AGW activity in January 2015 was associated with stronger polar vortex conditions (higher AO values). In contrast, weaker polar vortex conditions (lower AO values) in 2014 and 2016 allowed more diverse AGW spectra to reach mesospheric altitudes. These findings highlight the crucial role of stratospheric wind structures in driving AGW variability in the Arctic MLT region during winter.