Tidally Driven Intra-Seasonal Oscillations in the Thermosphere From TIEGCM-ICON and Connections to the Madden-Julian Oscillation

Abstract

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 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 uses an Ionospheric Connection Explorer (ICON)-adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model, 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 ($\sim$ 20 m/s) tidally driven ISOs throughout 2020–2021, largest at low latitudes $\left(\pm 30°\right)$ near 110–150 km altitude. Correlation analyses confirm a robust connection $\left(r>0.6\right)$ between thermospheric ISOs, tides, and the MJO. Additionally, Hovmöller diagrams show eastward tidal propagation consistent with the 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.