Climatology of Medium-Scale Traveling Ionospheric Disturbances Over Continental US Using GNSS TEC From 2012 to 2023

Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) have long been a subject of interest in ionospheric research. However, their spatiotemporal variability across regions, local times, seasons, and solar cycles is very complicated and remains not well established. Using Total Electron Content (TEC) data from global GNSS receiver networks processed at MIT Haystack Observatory, we perform a detailed statistical analysis of MSTIDs over the Continental US (CONUS). Differential TEC data every day from 2012 to 2023 are processed using a keogram-based image processing technique to identify MSTID wave properties, including the occurrence, propagation direction, phase speed, wavelength, and period. Focusing on eastern US midlatitudes (80°W, 40°N), we extend comparisons longitudinally and latitudinally across CONUS. Our results reveal significant variability in MSTID occurrence rates and propagation directions, notably linked to solar terminators. MSTID occurrence peaks after summer sunrise (with minor maxima near winter daytime), around summer sunset, and after summer midnight. Occurrence generally correlates positively with solar activity in summer but can become negative after winter midnight. In winter, MSTIDs propagate southeastward in the morning and rotate clockwise to west-northwestward after midnight; in summer, propagation is more variable. Comparisons across the CONUS highlight strong regional differences. Our findings reflect complex drivers behind MSTIDs, including gravity waves, electrodynamic processes, and solar terminators. Their relative influences vary with local time, season, and location. This long-term analysis provides critical insights into MSTID climatology and forms a basis for in-depth investigations of MSTID generation mechanisms.