Two-component phase scintillation spectra in the auroral region:
Observations and Model
Abstract
The random amplitude and phase fluctuations observed in
trans-ionospheric radio signals are caused by the presence of electron
density irregularities in the ionosphere. Ground-based measurements of
radio wave signals provide information about the medium through which
these signals propagate. The Canadian High Arctic Ionospheric Network
(CHAIN) Global Position System (GPS) receivers record radio signals
emitted by the GPS satellites, enabling the study of their spectral
characteristics.This study presents examples of phase spectra with two
power-law components. These components exhibit steeper spectral slopes
at higher frequencies and shallower ones at lower frequencies. In most
cases, the breaking frequency point is statistically larger than the
frequency associated with the Fresnel scale under the Taylor hypothesis.
To be more specific, we conducted a spectral characterization of sixty
(60) events recorded by the CHAIN Churchill GPS receiver, which is
located in the auroral oval. When fluctuations above the background
level are only observed in the phase, the spectra tend to be
systematically steeper. Conversely, the power increase in higher
frequency fluctuations accompanying amplitude scintillation tends to
result in shallower spectra. A basic yet powerful model of radio wave
propagation through a turbulent ionosphere, characterized by a power law
electron density spectrum, can help to explain the two power laws
observed in the scintillation events presented in this study by
identifying the role played by small-scale ionospheric irregularities in
diffraction.