Middle- and High-Latitude Mesosphere and Lower Thermosphere Mean Winds and Tides in Response to Strong Polar-Night Jet Oscillations

Abstract

The dynamical behavior of the mesosphere and lower thermosphere (MLT) region during strongly disturbed wintertime conditions commonly known as polar-night jet oscillations (PJOs) is described in detail and compared to other wintertime conditions. For this purpose, wind measurements provided by two specular meteor radars located at Andenes (69°N, 16°E) and Juliusruh (54°N, 13°E) are used to estimate horizontal mean winds and tides as an observational basis. Winds and tidal main features are analyzed and compared for three different cases: major sudden stratospheric warming (SSW) with (a) strong PJO event, (b) non-PJO event, and (c) no major SSWs. We show that the distinction into strong PJOs, non-PJOs, and winters with no major SSWs is better suited to identify differences in the behavior of the mean winds and tides during the boreal winter. To assess the impact of the stratospheric disturbed conditions on the MLT region, we investigate the 30-year nudged simulation by the Extended Canadian Middle Atmosphere Model. Analysis of geopotential height disturbances suggests that changes in the location of the polar vortex at mesospheric heights are responsible for the jets observed in the MLT mean winds during strong PJOs, which in turn influence the evolution of semidiurnal tides by increasing or decreasing their amplitudes depending on the tidal component. © 2019. The Authors.