Quiet Daytime Arctic Ionospheric D Region

Abstract

Phase and amplitude measurements of VLF radio waves propagating subionospherically 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, northward across the Arctic passing~2°from the North Pole, and then southward 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 U.S. Navy code LWPC, the daytime D region (Wait) height and sharpness parameters in the Arctic are found to be H 0 = 73.7 ± 0.7 km and β = 0.32 ± 0.02 km À1 in the summer of 2013, that is, at (weak) solar maximum. It is also found that, unlike at lower latitudes, very low frequency phase and amplitude recordings on (~1,000 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 nonsolar 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.Radio waves with frequencies of~10-40 kHz, that is, within and just above the very low frequency (VLF) range, have proved very valuable for measuring the lower D region (e.g., Thomson et al., 2014, 2017, and references

D‐Region High‐Latitude Forcing Factors

“…Figure shows the spatial configuration of the transmitter (NAA), the receiver (SOD), and the great circle propagation path between the transmitter and receiver (blue curve). The map shows that the majority of the VLF path is at latitudes poleward of 60°N and can thus be considered as representing high‐latitude conditions (Thomson et al, ). The thick boxes represent the regions around the VLF propagation path from where atmospheric temperature data were used (see section for details) in order to compare against the observations made on the VLF path.…”

Very Low Latitude Whistler‐Mode Signals: Observations at Three Widely Spaced Latitudes

“…The very low latitude whistler-mode signals, which are the prime focus of this report, can be clearly seen between~6 UT and~17 UT, that is, mainly during the night, particularly at Rarotonga, with group delays of~100 ms, tending to decrease by a few tens of ms during the night as the path (entry/height) slowly changes and the very low latitude ionosphere slowly decays (Thomson, 1987b). The indirect signals with constant delays~10-45 ms are from mountain range reflections, particularly here, at~30 ms, from the Rocky Mountains in the western United States/Canada (Thomson, 1985(Thomson, , 1989 (Thomson, 1993;Thomson et al, 2018, and references therein).…”

“…Journal of Geophysical Research: Space Physics ~1,000 μV/m. The amplitudes of the direct signals at Dunedin and Rarotonga were measured on site with a calibrated portable loop system (Thomson, 1993;Thomson et al, 2018, and references therein).…”

Electron Precipitation From the Outer Radiation Belt During the St. Patrick's Day Storm 2015: Observations, Modeling, and Validation

“…This is modeled through the Wait profile (Wait & Spies, 1964). Using high quality, absolute phase, multipoint measurements close to and far from individual transmitters, the nondisturbed quiet-time D-region reference height (H′) and sharpness (beta) parameters of the Wait profile have been found for low latitudes (Thomson et al, 2014), midlatitudes (Thomson et al, 2017), and high latitudes (Thomson et al, 2018). However, at the higher latitudes associated with the magnetic field-line footprints of the outer radiation belt, this has only been achieved for summertime, daylight conditions.…”