Quiet daytime Arctic ionospheric D region

• Published in: Journal of Geophysical Research: Space Physics
• Main Authors: Thomson, Neil R., Clilverd, Mark A., Rodger, Craig J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2018
• Subjects: Arctic; Norway; North Pole; Nome; Subarctic; Alaska
• Online Access: http://nora.nerc.ac.uk/id/eprint/521403/; https://nora.nerc.ac.uk/id/eprint/521403/1/Thomson_et_al-2018-Journal_of_Geophysical_Research__Space_Physics.pdf; https://doi.org/10.1029/2018JA025669

Phase and amplitude measurements of VLF radio waves propagating sub‐ionospherically on long paths across the Arctic are used to determine the high latitude, daytime D region height and sharpness of the bottom edge of the Earth's ionosphere. The principal path used is from the 23.4 kHz transmitter, DHO, in north Germany, northwards across the Arctic passing ~2° from the North Pole, and then southwards to Nome, Alaska, thus avoiding most land and all thick ice. Significant observational support is obtained from the also nearly all‐sea path from JXN in Norway (~67° N, 16.4 kHz) across the North Pole to Nome. By suitably comparing measurements with modeling using the US Navy code LWPC, the daytime D region (Wait) height and sharpness parameters in the Arctic are found to be H' = 73.7 ± 0.7 km and ß = 0.32 ±0.02 km‐1 in the summer of 2013 ‐ i.e., at (weak) solar maximum. It is also found that, unlike at lower latitudes, VLF phase and amplitude recordings on (~1000 km) paths at high subarctic latitudes show very little change with solar zenith angle in both phase and amplitude during daytime for solar zenith angles <~80°. It is concluded that, at high latitudes, the daytime lower D region is dominated by non‐solar ionizing sources in particular by energetic particle precipitation (>~300 keV for electrons) with a contribution from galactic cosmic rays, rather than by solar Lyman‐α which dominates at low and middle latitudes.