Intra-Seasonal Variability in Thermospheric Density and Winds and Possible Influences from Tropical Tropospheric Convection

The extent to which the thermosphere (ca., 100-500 km) is influenced by the lower (~0-20 km) and middle (~20-100 km) atmosphere from daily to monthly time scales is an important area of research that has escalated during the last two decades. Attaining a better understanding and characterization of intra-seasonal (IS, ~30-90 days) modes of variability in the thermosphere is increasingly recognized as a potential new source of whole atmosphere predictability. Recent observational and modeling-based studies suggest that a spectrum of upward propagating waves, including tides, gravity waves (GWs), and ultra-fast Kelvin waves (UFKWs), excited by deep convection in the tropical troposphere may be a leading driver of thermospheric IS variability. Tropospheric convection associated with the Madden‐Julian Oscillation (MJO) is the dominant mode of IS variability in tropical convection and circulation and has been shown to modulate the intensity of upward‐propagating tides, GWs and UFKW. In this work, spectral and temporal analyses of ~20-year of combined Challenging Minisatellite Payload (CHAMP), Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), and Swarm-C observations reveal prominent, persistent, and global-scale IS variability in middle thermospheric (~260-400 km) density and wind. Correlation analyses between these thermospheric IS variations and Outgoing Longwave Radiation (OLR) tropospheric data demonstrate at least nine large correlative events during 2000-2020. Nearly 15 years of continuous ground-based medium-frequency radar (MFR) zonal and meridional neutral wind measurements from Buckland Park, Adelaide (34.56°S, 138.48°E) are then used to investigate these IS variations in the ~70-100 km altitude region. Potential connections to wave driving and the MJO are discussed.