Tidally-driven intra-seasonal oscillations in the thermosphere from TIEGCM/ICON and potential connections to the Madden-Julian Oscillation

Recent evidence has revealed that strong coupling between the troposphere and the thermosphere (>100 km) occurs around intra-seasonal (IS, ~30-90 days) timescales. The Madden-Julian Oscillation (MJO), a dominant source of IS variability in tropical tropospheric convection and circulation, can influence the generation and propagation characteristics of solar tides and has been proposed as an important driver of thermospheric IS oscillation (ISOs). However, the sparsity of satellite observations in the `thermospheric gap' region (ca. 100-300 km), and thus numerical models incapable of accurately characterizing this region, has hindered our ability to improve our understanding of the fundamental processes at play. In this work, an Ionospheric Connection Explorer (ICON)-adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) with lower boundary tides based on Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) observations is used to quantify and characterize the impact of the upward-propagating tidal spectrum on thermospheric ISOs and reveal connections to the MJO. Thermospheric background zonal winds are shown to exhibit prominent (> +/- 10-20 m/s) tidally-driven IS oscillations, largest at low latitudes (30S-30N) in the 110-150 km altitude region and strongly (r=0.6) correlated with DE3 variability. Furthermore, IS variability in thermospheric DE3 amplitudes is found to share about 45% variance with the Real-time Multivariate MJO series 1 (RMM1) index. This study demonstrates that vertically propagating solar tides play a leading role in connecting IS variability from the lower atmosphere (below ~100 km) to the thermosphere and indicates the MJO to be the most likely contributor to this whole-atmosphere teleconnection.