Quiet Night Arctic Ionospheric D Region Characteristics

• Published in: Journal of geophysical research. Space physics Vol. 126; no. 4
• Main Authors: Thomson, Neil R., Clilverd, Mark A., Brundell, James B., Rodger, Craig J.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-04-2021
• Subjects: Atmospheric models; D region; Daytime; Electron precipitation; energetic electron precipitation; Equinoxes; galactic cosmic rays; geocoronal Lyman‐alpha; Ionization; Ionosphere; Ionospheric propagation; Night; Oceans; polar night D‐region electron density; polar night D‐region height and sharpness; Polar regions; Summer; VLF propagation; Arctic Ocean; Arctic region; Iceland
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2020JA029043

VLF radio propagation recordings are used to determine the characteristics of the nighttime polar lower D region of the ionosphere. Recordings of both VLF phase and amplitude in the Arctic on days within ∼1–2 weeks of the equinoxes enable their day‐to‐night changes to be determined. These changes are then combined with previously measured daytime polar D region characteristics to find the nighttime characteristics. The previously determined daytime characteristics were measured in the Arctic summer; the NRLMSISE atmosphere model is used to help determine the height change from daytime summer to daytime equinox (∼5 km lower). The principal path used was from the 16.4 kHz Norwegian transmitter JXN (67°N, 14°E) 1,334 km northwards across the Arctic Ocean to Ny‐Ålesund (79°N, 12°E), Svalbard. Also used were the 2,014‐km path from NRK (37.5 kHz, Grindavik, 64°N, Iceland) to Ny‐Ålesund, the 1,655‐km path from JXN to Reykjavik (64°N, Iceland), and the 5,302‐km path from JXN across the Arctic Ocean to Fairbanks (65°N) in Alaska. The night values of (the Wait parameters) H′ and β were found to average from ∼79 km at equinox down to 77 km near winter solstice (lower than the 85 km at low and midlatitudes by ∼7 km) and 0.6 km−1, respectively. This lower height and its variability are shown to be consistent with the principal source of ionization being energetic electron precipitation.
Key Points
Arctic VLF radio propagation recordings enable the characteristics of the nighttime polar D region to be inferred
The undisturbed night Arctic D region is more variable and occurs at lower altitudes (∼78 km), than at lower latitudes (∼85 km)
The polar D region is maintained mainly by electron precipitation rather than by Lyman‐alpha or galactic cosmic rays