Characterizing ionospheric variability through HF Doppler measurements: a statistical and numerical ray tracing analysis

High-frequency (HF) skywave propagation relies on the ionosphere, making it susceptible to ionospheric variability. This study analyzes long-term Doppler residual measurements of a 10 MHz HF link between Fort Collins, CO, and Newark, NJ, to characterize the impact of ionospheric conditions on the link. We report that daytime measurements of Doppler variability exhibit Cauchy statistics, while nighttime measurements show a combination of exponential and log-normal statistics. These patterns correlate with solar activity and solar zenith angle. We also use PHaRLAP numerical ray tracing simulations through the IRI 2020 ionosphere to provide insights into signal ray paths and the altitudes of the ionosphere contributing to the observed Doppler shifts. By examining diurnal variations and statistical properties of Doppler residuals, this study aims to enhance our understanding of ionospheric dynamics and their influence on HF signal characteristics.