Improved Detection of Traveling Ionospheric Disturbances using Optimal Line-of-sight Geometries of Total Electron Content Measurements

Traveling ionospheric disturbances (TIDs) often have distinct characteristics based on the physical process driving them, which include geomagnetic storms, electrodynamic effects, and tropospheric phenomena such as earthquakes, volcanic eruptions, and severe convective weather systems like thunderstorms and hurricanes. As the ionosphere is a highly dynamic region, TIDs originating from multiple sources can be present simultaneously, potentially overlapping and complicating observational analyses.
Total electron content (TEC) measurements are among the most effective methods to observe the horizontal characteristics of TIDs, but the geometry of these measurements, defined by the receiver-satellite line-of-sight (LOS) elevation and azimuth angles, varies depending on satellite position relative to the receiver. However, previous studies typically treat all measurements as equivalent, overlooking geometry differences, but the LOS alignment relative to electron density fluctuations can significantly impact TID characterization from TEC observations.
Our previous work has identified LOS geometries that are optimal for observing concentric TIDs induced by gravity waves (GWs) from tropospheric convective sources, by finding the LOSs that best align with the electron density fluctuations. This study aims to identify and explain the optimal LOS geometries for TIDs driven by a wider variety of sources, such as non-concentric daytime MSTIDs, nighttime electrified MSTIDs, or TIDs driven by processes originating above the ionosphere. Each of these TIDs can have a preferred observing geometry based on their characteristics such as propagation direction and the tilt of their phase fronts. In this study, we present TEC maps illustrating various types of TIDs, comparing their detectability when constructed using all LOSs irrespective of their geometries, only optimal geometries, and non-optimal geometries. Additionally, we explain why and how the optimal observing geometries differ among various TID types.
Using the optimal LOS geometry when observing TIDs is important for an accurate representation of these ionospheric features in the F-region. Moreover, in scenarios involving overlapping TIDs from multiple sources, using knowledge of optimal LOS geometries can help isolate disturbances from individual sources, reducing interference and enabling a more detailed and accurate analysis. Ultimately, this research advances our understanding of TEC-based TID observations and contributes significantly to refining observational methodologies for studying ionospheric disturbances.