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Low-latitude ionospheric D region dependence on solar zenith angle

Thomson, Neil R.; Clilverd, Mark A.; Rodger, Craig J.. 2014 Low-latitude ionospheric D region dependence on solar zenith angle. Journal of Geophysical Research: Space Physics, 119 (8). 6865-6875. 10.1002/2014JA020299

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Abstract/Summary

Phase and amplitude measurements of VLF radio signals on a short, nearly all-sea path between two Hawaiian Islands are used to find the height and sharpness of the lower edge of the daytime tropical D region as a function of solar zenith angle (SZA). The path used was from U.S. Navy transmitter NPM (21.4 kHz) on Oahu to Keauhou, 306 km away, on the west coast of the Big Island of Hawaii, where ionospheric sensitivity was high due to the destructive interference between the ionospherically reflected wave and the ground wave, particularly around the middle of the day. The height and sharpness are thus found to vary from H′ = 69.3 ± 0.3km and β = 0.49 ± 0.02 km�1 for SZA ~10°, at midday, to H′ >80 km and β ~ 0.30 km�1 as the SZA approached ~70°–90°, near dawn and dusk for this tropical path. Additional values for the variations of H′ and β with solar zenith angle are also found from VLF phase and amplitude observations on other similar paths: the short path, NWC to Karratha (in NW Australia), and the long paths, NWC to Kyoto in Japan and NAU, Puerto Rico, to St. John’s Canada. Significant differences in the SZA variations of H′ and β were found between low and middle latitudes resulting from the latitudinally varying interplay between Lyman α and galactic cosmic rays in forming the lower D region. Both latitude ranges showed β<0.30 km�1 during sunrise/sunset conditions. 1.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1002/2014JA020299
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Climate
ISSN: 21699380
Date made live: 17 Dec 2014 09:27 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/509124

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