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oai:figshare.com:article/34054488 2026-10-02T05:35:50Z category_57 portal_316 item_type_3 month_year_10_2026

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 Danielle G. Markowski (25162509) Stephen R. Kaeppler (11546920) Cosmology day-to-day variability geomagnetic activity HF propagation ionosphere traveling ionospheric disturbances <p>Since the early 1960s, many studies have documented ionospheric virtual height oscillation with periods ranging from 30 min to 3 h. However, in this investigation, we find a consistent, much larger period in the oscillations of virtual height, as estimated using Coastal Ocean Dynamics Applications Radars (CODARs), whereas few previous studies have consistently observed periods of oscillation in this range. The purpose of this investigation is to investigate day-to-day bottomside variability, and we report a consistently observed 4–5-h period of virtual height oscillation, along with providing potential physical interpretations of the observations. We use bistatic high-frequency data from CODARs, collected nearly continuously between 2020 and 2023 at a 2-min time cadence. The frequency modulated continuous wave (FMCW) waveforms of these radars are suitable as a single-frequency oblique ionospheric sounder. We estimate the group delay from which the virtual height of an ionospheric layer can be estimated. 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> 2026-10-02T05:35:50Z Dataset Dataset 10.3389/fspas.2026.1886813.s001 https://figshare.com/articles/dataset/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/34054488 CC BY 4.0