Data Sheet 1_Observations of 4–5 h oscillation periods in virtual height during the fall seasons of 2020–2023 across the eastern United States.pdf

We present statistical results from several virtual height oscillations with varying periods across September, October, November, and December during 2020–2023. For each year, we compare three to four CODAR transmitters located in the Eastern United States, operating at 4–5 MHz. The receiver is located near Clemson University.

We frequently observe (≈ 25% of the time) the 4–5-h period of virtual height oscillation each September through December over the 4-year span, which has a longer period than the standard categorization of a Large Scale Traveling Ionospheric Disturbance (LSTID). To further understand the characteristics of these structures, we separate them into both propagating and non-propagating structures. We found that for all 4–5-h structures with southward propagation, the night prior was geomagnetically active.

We also find significant similarities between the non-propagating structures and two ionospheric phenomena, the midnight collapse and post-midnight enhancement.</p>