Ray-tracing the paths of very low latitude whistler-mode signals |
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| Institution: | 1. College of Automation, Harbin Engineering University, Harbin 150001, China;2. Institute of Remote Sensing in BEIJING, Beijing 100192, China;1. State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China;2. City University of Hong Kong, 999077, Hong Kong Special Administrative Region;1. National Research Institute of Astronomy and Geophysics (NRIAG), 11421, Helwan, Cairo, Egypt;2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA;3. Astronomy, Space Science and Meteorology Dept., Faculty of Science, Cairo University, Giza, Egypt;1. Center of Space Technologies, Institute of Aviation, Aleja Krakowska 110/114, 02-256 Warsaw, Poland;2. Institute of Heat Engineering, Warsaw University of Technology, Nowowiejska 21/25, 00-665 Warsaw, Poland |
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| Abstract: | VLF whistler-mode signals with very low group delays (75–160 ms) received at night in Dunedin, N.Z., from the 23.4 kHz MSK transmissions of NPM, Hawaii (21.5°N, 158°W), are explained by ray-tracing along unducted paths. The typical vertical and horizontal electron density gradients of the night equatorial ionosphere are found to be sufficient to explain not only the typical group delays but also their decrease during the night and the typical frequency shifts observed on these signals. An important feature appears to be the decreasing starting and finishing latitudes (and the decreasing maximum height of the path) during the course of the night. The amplitude of the signals in relation to the expected collisional absorption in the ionosphere is discussed. A simple but quite accurate analytical expression suitable for ray-tracing is derived for the night electron density in the height range 170–1400 km, based on non-isothermal diffusive equilibrium and O+/O friction. |
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