Recent evidence has revealed that strong coupling between the lower atmosphere and the thermosphere ($>$100 km) occurs on intra-seasonal (IS) timescales (~30-90 days). The Madden-Julian Oscillation (MJO), a key source of IS variability in tropical convection and circulation, influences the generation and propagation of atmospheric tides and is believed to be a significant driver of thermospheric IS oscillations (ISOs). However, limited satellite observations in the ‘thermospheric gap’ (100-300 km) and challenges faced by numerical models in characterizing this region have hindered a comprehensive understanding of this connection. This study utilizes an ICON-adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), incorporating lower boundary tides from Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) observations, to quantify the impact of the upward-propagating tidal spectrum on thermospheric ISOs and elucidate connections to the MJO. Thermospheric zonal and diurnal mean zonal winds exhibit prominent (~20 m/s) tidally-driven ISOs throughout 2020-2021, largest at low latitudes ($\pm$30$^\circ$) near 110-150 km altitude. Correlation analyses (r>0.6) confirm a robust connection between thermospheric ISOs, tides, and the MJO. Additionally, Hovmoller diagrams show eastward tidal propagation consistent with MJO and concurrent Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. This study demonstrates that vertically propagating tides play a crucial role in linking IS variability from the lower atmosphere to the thermosphere, with the MJO identified as a primary driver of this whole-atmosphere teleconnection. Understanding these connections is vital for advancing our knowledge in space physics, particularly regarding the dynamics of the upper atmosphere and ionosphere.

Recent evidence has revealed that strong coupling between the lower atmosphere and the thermosphere ($>$100 km) occurs on intra-seasonal (IS) timescales ($\sim$30-90 days). The Madden-Julian Oscillation (MJO), a primary source of IS variability in tropical tropospheric convection and circulation, can influence the generation and propagation characteristics of atmospheric tides and has been proposed as a significant driver of thermospheric IS oscillations (ISOs). Despite this progress, the limited availability of satellite observations in the ‘thermospheric gap’ region (ca. 100-300 km) and the inability of numerical models to accurately characterize this region have hindered a comprehensive understanding of this connection and the fundamental processes involved. In this study, an Ionospheric Connection Explorer (ICON)-adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), incorporating lower boundary tides derived from MIGHTI observations, is utilized to characterize and quantify the impact of the upward-propagating tidal spectrum on thermospheric ISOs and to elucidate connections to the MJO. Thermospheric zonal and diurnal mean zonal winds are shown to exhibit prominent ($\sim$20 m/s) tidally-driven ISOs throughout 2020-2021, largest at low latitudes ($\pm$30$^\circ$) near $\sim$110-150 km altitude. Correlation analyses demonstrate a robust (r$>$0.6) connection between the thermospheric ISOs, tides, and the tropospheric MJO, moreover, Hovm\”oller diagrams indicate eastward tidal propagation consistent with the MJO and concurrent SABER observations. This study demonstrates that vertically propagating tides play a crucial role in linking IS variability from the lower atmosphere to the thermosphere, with the MJO identified as a primary contributor to this significant whole-atmosphere teleconnection.