Multi-instrument study of the mesosphere-lower thermosphere dynamics at 80°N during the major SSW in January 2019

Abstract

Contemporaneous multi-instrument ground-based optical and meteor radar observations of OH and O2 airglow, temperature and neutral winds during the winter season of November 2018–February 2019 have been used to investigate the dynamics of the mesosphere/lower thermosphere (MLT) (80–100 km) region in the high Arctic at Svalbard, Norway (78°N, 16°E) and at Eureka, Canada (80°N, 274°E). Temperature observations by the MLS Aura satellite over the 20–90 km height range for the same period were also considered. The period is characterized by an unusual major sudden stratospheric warming (SSW) event that began with a displacement of the polar vortex around December 13, 2018 (DoY 347), followed by the vortex split on January 2, 2019 (DoY 367). The MLS Aura temperature observations outlined four periods of interest: 1) late November – early December (DoY 328–335) with cold temperature anomalies in the mesosphere and warm bursts at the stratopause; 2) December 13, 2018–January 2, 2019 (DoY 347–367) when the stratopause rapidly descended to 45 km and broke down, triggering the onset of a SSW; 3) January 3–20, 2019 (DoY 368–385) during the stratopause recovery phase, and 4) from January 21, 2019 (DoY 386) onward, with the formation of the elevated stratopause and gradual return to its pre-SSW height. Both airglow emissions, OH and O2 Atm, showed simultaneously significant depletion of the integrated emission rates (IER) and temperature decrease of the order of 50–60 K, indicating upwelling, depletion of the atomic oxygen and adiabatic cooling. These cold temperature anomalies were followed by enhancements in the observed airglow IERs on December 13, 2018 (DoY 347) and January 2, 2019 (DoY 367) accompanied by a decrease in the peak altitude of the OH layer suggesting down-welling and influx of atomic oxygen from the lower thermosphere. The observations revealed oscillations with periods of 4.5–7 days, 8–10 days, and 16–21 days consistent with previously reported planetary wave activity in the winter MLT region and during major stratospheric warming events. However, the results presented here show for the first time comparisons of the multi-instrument temperature observations at 78°N – 80°N, providing an indispensable tool in monitoring the dynamics over the polar cap in general, and in describing the regional dynamical response of the MLT region to major large-scale phenomena like stratospheric warmings, in particular.