Terdiurnal atmospheric tides seen with ICON at E- and F-region altitudes

The Earth's upper atmosphere is highly dynamic, serving as a crucial interface between tropospheric weather processes and the exosphere. Understanding its variability is essential for assessing its impact on lower atmosphere and its response to space weather. A comprehensive approach to the exploration of the features of the ionosphere is to observe the global-scale waves known as atmospheric tides and planetary waves which influence and also generate similar wave-like disturbances in the E- and F-region altitudes. While previous studies suggest that tides migrate upwards and cause changes in the ion production, loss and transport in the ionosphere, further investigation is necessary to quantify these effects. The MIGHTI instrument aboard the ICON satellite provides three years of global wind and temperature data (2019-2022) spanning altitudes from 90-300 km and latitudes from 6°S to 42°N during day and night local times. Using this dataset, the study examines the effects of terdiurnal tides on the ionosphere
and its seasonal and annual patterns are observed.

A key enabling factor for this objective is to use tidal fits to a wave model which assists in simulating various ionospheric regions so that different tidal patterns can be observed. The structural approach for the study involves developing an elaborate wave model which is a sine wave with amplitude and phase components of each tide that have temporal periods of 24, 12 and 8 hours, (n), and zonal wavenumbers ranging from -6 to 6, (s). Further computation involves reconstructing the desired tides from the obtained values and analyzing them along varying times, altitudes and latitudes. The results are compared with previous studies and conclusions are drawn. Uncertainty in amplitudes and phases are also accounted for to explain potential variations in observations or digressions from anticipated results.

Initial findings indicate that the bulk of the E-region altitudes consist of diurnal and semidiurnal tides with the zonal wind amplitudes peaking at 50 m/s near the equator. Preliminary analysis for the migrating terdiurnal tide (TW3) reveals well-defined structures in the F-region with zonal wind amplitudes reaching up till 70 m/s. This suggests that these might be generated somewhere in the mid-altitudes. Ongoing work addresses altitude-dependent variations and discrepancies, considering factors such as limited nighttime data at high altitudes and dominance of other tides at low altitudes which possibly cause terdiurnal tides to be more sensitive to minor amplitude fluctuations and therefore harder to extract. Further research aims to refine these conclusions and enhance our understanding of terdiurnal tidal variability in the ionosphere, aiding space weather forecasting, satellite operations, and communication reliability. Refined tidal models that provide reliable results benefit scientists, space agencies, and navigation experts in mitigating ionospheric disturbances, improving GPS accuracy, and optimizing satellite performance, ultimately contributing to advancements in atmospheric science and space technology.