科研之友
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摘要
Observed phases and amplitudes of VLF radio signals propagating on very long paths are used to validate electron density parameters for the lowest edge of the (D region of the) Earth's ionosphere at low latitudes and midlatitudes near solar minimum. The phases, relative to GPS 1 s pulses, and the amplitudes were measured near the transmitters (similar to 100-150 km away), where the direct ground wave is dominant, and also at distances of similar to 8-14 Mm away, over mainly all-sea paths. Four paths were used: NWC (19.8 kHz, North West Cape, Australia) to Seattle (similar to 14 Mm) and Hawaii (similar to 10 Mm), NPM (21.4 kHz, Hawaii) and NLK (24.8 kHz, Seattle) to Dunedin, New Zealand (similar to 8 Mm and similar to 12 Mm). The characteristics of the bottom edge of the daytime ionosphere on these long paths were found to confirm and contextualize recently measured short-path values of Wait's traditional height and sharpness parameters, H' and beta, respectively, after adjusting appropriately for the (small) variations of H' and beta along the paths that are due to (1) changing solar zenith angles, (2) increasing cosmic ray fluxes with latitude, and (3) latitudinal and seasonal changes in neutral atmospheric densities from the (NASA) Mass Spectrometer Incoherent Scatter- (MSIS-) E-90 neutral atmosphere model. The sensitivity of this long-path (and hence near-global) phase and amplitude technique is similar to +/- 0.3 km for H' and similar to +/- 0.01 km(-1) for beta, thus creating the possibility of treating the height (H' similar to 70 km) as a fiduciary mark (for a specified neutral density) in the Earth's atmosphere for monitoring integrated long-term (climate) changes below similar to 70 km altitude.
- 出版日期2011-11-2
- 单位British Antarctic Survey
