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- Title
High‐Latitude Off‐Great Circle Propagation Associated With the Solar Terminator.
- Authors
Cameron, T. G.; Fiori, R. A. D.; Perry, G. W.; Ruck, J. J.; Thayaparan, T.
- Abstract
Large‐scale ionospheric gradients associated with the solar terminator can deflect high frequency (HF) radio waves to off‐great circle paths during the morning and evening, negatively impacting technologies reliant on HF radio wave propagation. For example, geolocation algorithms used by scientific and military over‐the‐horizon radars (OTHRs) generally assume on‐great circle propagation, and thus lateral deviations from the great‐circle path can lead to positioning errors. In this study, radio wave propagation is simulated via 3D numerical ray traces though an empirical, high‐latitude model ionosphere initialized for a variety of times of the day and year to explore and quantify high‐latitude off‐great circle propagation associated with the solar terminator. Analysis of these simulations show large scale east‐west ionospheric gradients due to the solar terminator can cause lateral deviations in north‐directed propagation paths exceeding 20° at sunrise and sunset depending on radio wave frequency, though the largest portion of received signal power tends to experience maximum deflections of 5°. An exploration of the dependence of propagation direction on deflection shows that propagation paths parallel to the solar terminator tend to experience the largest deflections. Since the solar terminator at high latitudes is at an angle with respect to north in the winter and summer, propagation paths oriented west or east of north can experience larger deflections than north oriented paths at sunrise and sunset during these times of year. Impacts of these diurnal deflections on the operation of OTHR and scientific radar are discussed, as well as possible strategies for mitigating them. Plain Language Summary: High frequency (HF) radio waves are able to travel long distances by bouncing between the ionosphere (an upper layer of the Earth's atmosphere) and the ground. HF radio waves transmitted north can have their paths deflected east or west by changes in the ionosphere that happen at sunrise and sunset. In this paper, simulations of radio waves are used to explore how large these deflections can be and how they change over the course of the day and year. It is found that north pointing radio signals at certain frequencies can be deflected by more than 20° at sunrise and sunset. These simulations are also used to explore how radio waves transmitted in different directions are deflected at sunrise and sunset. It is found that radio waves transmitted along the dividing line between day and night tend to experience the largest deflections. The Earth is tilted with respect to its rotation, meaning this dividing line is not always aligned with North. The deviation from north is largest in the winter and summer. This means that radio waves transmitted west or east of north at these times of year can experience larger deflections than northward transmissions. Key Points: The lateral deflection of high frequency radio waves caused by the solar terminator is investigated with ray tracing simulationsNorth‐south propagation paths can experience significant (>20°) deflections in the morning and eveningEast‐west paths can also see significant deflections at high latitudes, at times when the solar terminator is also oriented east‐west
- Subjects
RADIO wave propagation; RADIO waves; SHORTWAVE radio; SUNRISE &; sunset; SOLAR radio emission; LATITUDE; ATMOSPHERICS
- Publication
Radio Science, 2024, Vol 59, Issue 5, p1
- ISSN
0048-6604
- Publication type
Article
- DOI
10.1029/2023RS007917