Quiet Night Arctic Ionospheric D Region Characteristics

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 similar to 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 (similar to 5 km lower). The principal path used was from the 16.4 kHz Norwegian transmitter JXN (67 degrees N, 14 degrees E) 1,334 km northwards across the Arctic Ocean to Ny-angstrom lesund (79 degrees N, 12 degrees E), Svalbard. Also used were the 2,014-km path from NRK (37.5 kHz, Grindavik, 64 degrees N, Iceland) to Ny-angstrom lesund, the 1,655-km path from JXN to Reykjavik (64 degrees N, Iceland), and the 5,302-km path from JXN across the Arctic Ocean to Fairbanks (65 degrees N) in Alaska. The night values of (the Wait parameters) H ' and beta were found to average from similar to 79 km at equinox down to 77 km near winter solstice (lower than the 85 km at low and midlatitudes by similar to 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.

Automated summary

VLF radio propagation recordings are used to determine the characteristics of the nighttime polar lower D region of the ionosphere. By analyzing VLF phase and amplitude recordings in the Arctic, researchers were able to determine the day-to-night changes near the equinoxes. The study found that the lower height of the ionosphere at night and its variability are consistent with energetic electron precipitation being the main source of ionization.