Ultra-Fast Tropical Wave-Induced Variability, Interaction, and Vertical Coupling in the Ionosphere-Thermosphere-Mesosphere

The equatorially trapped eastward propagating waves with periods of less than a week in the lower atmosphere are generally called ultra-fast tropical (UFT) waves. Among these, the eastward-propagating 2-, 3-day ultra-fast Kelvin waves (UFKWs) wave and the eastward-propagating diurnal tide with zonal wave number 3 (DE3) are of scientific attention and represent key characteristics of UFT waves originated from the tropical troposphere. Numerous studies have reported that the pattern of tropical troposphere variability effectively extends into the ionosphere-thermosphere (IT) system through a variety of interaction and coupling processes, spanning different spatial and temporal scales. However, due to limited global observations and modeling efforts, there remain many unanswered questions regarding the sources, variability, interaction, and coupling of UFT waves within the IT system.
In this investigation, we utilize temperature, wind, and density data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), the Ionospheric Connection Explorer (ICON) - Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI), and the Swarm-C satellites, respectively. The daily amplitudes of UFTW (mainly DE3 and UFKW1) are extracted from satellite data as a function of latitude throughout 2020 and 2021. Additionally, the physics-based High Altitude Mechanistic General Circulation Model (HIAMCM) has the ability to reproduce UFKW events spanning from the Earth’s surface/troposphere up to an altitude of approximately 450 km. It can be employed to understand the nature of the ionospheric variability caused by the wave activity in the lower atmosphere. The UFKW-induced variability in satellite-observed amplitudes of temperature, wind, and neutral density will be compared with those modeled by the HIAMCM. This comparison will help to estimate the degree to which the model captures their interactions and variabilities in the mesosphere, thermosphere, as well as the ionosphere. Specifically, we evaluate the vertical profiles of these wave spectra (UFKW and DE3) across multiple altitudinal ranges to address abovementioned debatable questions regarding UFT wave-induced variabilities, interactions, and coupling from the lower atmosphere to the ionosphere.