Identifying Scales of the Ionospheric Structure Through Scintillation Events

Abstract

In the polar regions, ionospheric electron density structures are known to develop as a result of plasma instabilities driven by currents and pressure gradients. These plasma structures are typically investigated through in situ observations using instruments aboard spacecraft and rockets. In addition, measurements recorded by ground-based Global Navigation Satellite System GNSS receivers provide valuable indirect data about the impact of ionospheric irregularities on the propagation of radio waves emitted by satellites. At high latitudes, the Canadian High Arctic Ionospheric Network records fluctuations in the amplitude of trans-ionospheric radio signals from GNSS satellites, which are then analyzed to determine the characteristic length scales of the ionospheric plasma. Probability distributions of these fluctuations are constructed across frequency ranges. The distributions are found to be well-described by the Castaing function, which was introduced in the context of fluid dynamics to describe the distribution of velocity fluctuations in two-dimensional neutral fluid turbulence. Our analysis reveals that the Castaing distribution scale parameter decreases as the frequency of amplitude fluctuations increases, meaning that only high-frequency amplitude fluctuations conform to Gaussian statistics. For some scintillation event cases, a Gaussian distribution is observed at frequency scales where the signal power density level falls below the instrumental noise level. The results of our study suggest that the radio wave propagation occurred through an ionospheric layer with a weak electron density gradient, yet abundant in small-scale electron density structures. These results also suggest that a plasma dynamical equilibrium is reached only when small scales dominate the interaction processes in the plasma.