Decadal Trends of Non-Migrating Eastward-Propagating Diurnal Tides in the MLT Region

Vertically propagating tides and other waves of tropospheric origin are leading drivers of long-term variability and dynamical coupling in the ionosphere-thermosphere-mesosphere (ITM) system. This study explores the decadal trends, variability, and coupling of the dominant non-migrating eastward-propagating diurnal (DE) tides in the mesosphere and lower thermosphere (MLT) region. The non-migrating tides are excited by differential solar heating, deep tropospheric convection over the tropics releasing latent heat, and nonlinear interactions between migrating tides and planetary-scale waves. These tides are important for understanding the complex interplay between upward-propagating waves of lower atmospheric origin and the coupling between terrestrial weather and space weather across different atmospheric layers on various timescales.

Utilizing long-term temperature observations from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) in the MLT region, and simulated results from the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X), we identify decadal trends in DE tidal amplitudes and phases over the past 22 years (2002-2023). During the course of vertical propagation, the competing role of DE tides in the modulation of the E-region dynamo will be examined, which ultimately impacts the space weather of the ionosphere. This analysis also evaluates the impacts of the solar cycle (SC), quasi-biennial oscillation (QBO), semiannual oscillations (SAO), and El Niño–Southern Oscillation (ENSO) on non-migrating diurnal tides. The observed trends are further examined in the context of simulation results from WACCM-X to understand the physical mechanisms that transmit long-term variability from the lower atmosphere into the ITM system. This study emphasizes the importance of understanding long-term trends in tidal waves to advance knowledge of the interconnections between terrestrial and space weather processes across different spatial and temporal scales and for improving predictive models of upper atmospheric conditions, which are crucial for mitigating space weather impacts on modern technologies.